We live near a small town in Texas, and the feed store is the heart of the town. You may want to follow their "marketing plan".
1. Any local that sells non-perishable produce like potatoes or onions can sell through the store for a small percentage.
2. Have a bulletin board where farmers can post equipment and livestock for sale.
3. Find someone who can repair trimmers, snowblowers, lawnmowers and tillers, and who will sharpen blades and offer to advertise that service out-of-store, but the store is a drop-off point. Gets people in, you know.
4. Have a coffee pot going. Those who stand around jawing eventually buy. You can even have a coffee can for dimes and quarters for those who wish to contribute.
5. Any church or local group that is having a raffle, bake sale or spaghetti supper, offer your front window to display a flyer.
6. If there is a local gardening club or Master Gardeners association, contact them and see what seeds, tools, equipment they recommend. Then if you stock XXX brand seeds, put up a little hand-lettered notice "recommended by the Green Thumb Garden Club".
7. Finally, if there is another store that offers tillers, snowblowers, trimmers, etc. don't try to compete with the same brand. Folks get used to buying where they bought before, and if you offer the same thing, your wares will gather dust. Good luck with your venture!

I just visited a friend's store and was really blown away by the atmosphere and just loved it. It started as an antique type place and evolved to a place where local artists and collectors could rent booths to display their wares. No junk/yard sale stuff allowed and she has the yay/nay over what is displayed. She always had coffee going in the morning and the very tables/chairs that were for sale were decorated beautifully for people to sit at in the morning. That also evolved to having a sweet pastry that she made in the morning to serve with the coffee. She and her partner just got approved to start serving a simple luncheon, usually soup and sandwiches. The shop is gorgeous. She has different areas like the "quilting room," where people display those types of items and has a sitting room where they can host quilting meetings or parties. I'm not saying you should be interested in serving food and the like but definitely the coffee pot in the morning as the previous poster mentioned is a way to get people in. As a gardener I would love to see various types of heirloom seeds and seeds/products proven to work in my local area. Lori

If you are going to have horse trailers, how about some basic horse supplies. Wormers, brushes, treats, water buckets, etc ...

Bird seed in the fall, flower seed in the spring.

Basic hardware for a farm.

A store I used to go to locally had different types of animal food, for pigs, goats, chickens, etc.

You could also sell nursery stock, shrubs, perennials, etc spring through fall - not the common annuals that everyone has, but the serious gardener stuff and equipment - shovels, rakes, etc.

You could have a local artisan section where locals could sell wares through the store on consignment, you keep 30%.

Pond supplies, liners, pumps and even goldfish, snails and tadpoles (nothing fancy) in the spring. You might want to put in a pond where you can store this stuff over the winter or put the pond out front and also use it for display.

Be a chick order place for a majoy hatchery, with your own mark-up, of course. Our co-op is where we go to order chicks or grown hens. They don't keep them in stock, but purchase them as ordered from Frey's hatchery, paid in advance, to be picked up on delivery day.

If you wanted to get into other related areas you could sell common landscaping supplies, the large lightweight rocks, arbors, benches, birdbaths, statues and fountains, etc.

Offer the services of a professional landscaper through your store.

Pet and farm animal feed is a very good thing to get into.

Homemade soap and candles.

Homemade relishes and jams, canned in mason jars. Lots of Mennonite type communities have these for sale.

Here is a link that might be useful: My Country DIY Blog

Focus!

Keep your focus.

Doesn't mean no variety, but decide on an image, and everything connects to that image.

Who is your target market?

What overall is your product?

From what you've said:
1. A rental store. If you do this, you rent everything from shovels to bobcats. For large items, have a $20 delivery fee/pickup fee. To do this you need someone on site that can repair almost everything. Ball park figure is that something rents for 1% of it's cost per day.

Your market is the acreage owner who needs a wood splitter for 3 days every fall, and a chipper for a weekend in the spring. And the home handyman with a fixer-upper.

2. A craft store. Your own, and your neighbors crafts. Figure out what a shelf has to make per month. That becomes the basis for rent. Unless you want to go crazy you either have to have some bar code system so that you can later tell Michelle that 42 jars of the crabapple-blueberry jelly sold, but none of the Green tomato mincemeat. OR you have to buy the stuff from them wholesale, and resell it. The latter is simpler, more profitable, but higher risk.

3. Coffee spot. Baked goods. This one combines well with a craft store, not so much with a rental store.

4. Hardware store. Bulk hardware. (Our UFA store sells a lot of hardware by the pound. E.g. Any size nail is 60 cents a pound. All nuts and bolts and washers are 2.35 a pound. All deck screws ... ) If you do hardware you should carry a full line of fencing stuff too. We have a category of stores that for lack of a better term I'll call farm stores. UFA, Co-op, Peavey Mart. They are far larger than 2600 square feet. Probably 15,000-25000 square feet plus a yard. Combine a lumber store, ag chemical store, hardware store (but limited) They will sell curry combs, but not saddles. Ear tags and milk supplement. Chicken grit. Can buy pipe and a sink, but not a fancy sink. Can buy paint, but only in fixed colours. Red and white are available in 5 gallon buckets. Can buy motor oil, but not oil filters. Can buy calf sleds.

5. If you go with trailer rental, you need an acre outside the place to store them. True for lots of big item rental.

If you want it to be a store that people enjoy you need a product that they come in for over and over. This implies some form of consumable item. -- food, nails.

When you open a retail store, you are on a leash. You have to keep the same hours that your neighbors do. Our small town runs 9 a.m. to 6 p.m. 6 days a week, except Thursday and Friday they are open until 9 p.m. Only coffee spots are open on Sunday.

Exceptions: The rental store is open at 7 a.m. so that the foreman can pick up that generator on the way to the job site.

You or someone you trust have to be there every moment of that day.

Story time:
This year I did test marketing for Cut your own Christmas Tree. I had a small mention on my web site, and a small unpaid ad on PickYourOwn.org. I got 50 contacts, and sold a dozen trees over 3 weekends. One weekend was bitter cold (-30) and all 8 people cancelled.)

We did it by appointment. That way we'd know when to expect people. One of us was in the hosue to answer the phone from half an hour before to half an hour after their appointment time when they got lost. (No such thing as fool proof directions... Fools are too clever.)

I work out of my house. Even so, my weekends were circumscribed by the need to be around. It's hard to do much else when running a retail business. You can do other things, but your attention is always split.

Will I do it again? Yes. The market is there. Based on my very limited advertising, I think I can ramp up to 40-60 trees per weekend for the month prior to Christmas. At that level, I can handle the entire operation with my better half at home with the phone, and myself in the field with the trees.

If I hired high school kids in elf hats, I could go bigger than that, but I'm not sure I want to.

In the beginning focus on items that relate to the equipment you will be renting. Add a few items one or two at a time and see which ones are selling. If they don't sell find a way to get rid of them. Find a store that sells the item and offer your stock to them at a discount. Always look for items that you can return to the seller if it doesn't sell. Remember, it takes a while to find your niche in the market. Oh yes! Check into selling utility trailers. They sell pretty well here in farm and ranch country. We have two equipment rental places in my little town. One concentrates on large equipment like backhoes and the other on small equipment like mowers and tillers. If there isn't another rental place in your area you could have both kinds of equipment.
After you've established your focus customer base then branch out into other type items a few at a time to "test the waters" as far as saleability in your area.

If you are stocking horse trailers, look into stalldry. I use it at the clinic for cat litter & all my animals. Takes care of ammonia & wetness which is bad on trailers & animals too.