Tires = free at a dealer. You'll just have to transport it, pickups are great, may have to rent a U-haul for a day.
Kegs = free. Easiest way to deal with them is have a welder cut off the tap part and put on a short piece of 2" threaded pipe and use a screw-on cap. Easy to adjust.
Farmer's walk - ontario strongman has a great description of how to make tightwad implements.
Stones - actual stones are fairly expensive just by nature of materials and the molds. I'd advise going natural rock hunting at first, then saving up for a few. Where are you? The less shipping the better; talk to Murph at TPS in the New England area or Art McDermott if he's distributing (not sure).
Yoke - you COULD make one if you have the necessary tools, but if not, Alumatech makes a great model that you can take apart for storage.
Log - buying one is just about as cheap as making one, honestly, unless you happen to already have a lot of steelworking tools.
Southern Strongman makes good logs and a cool combo Viking Press/Car deadlift/Conan's wheel thing, I'd advise checking it out.
Sandbags are free, too, or cheap to buy a duffel and some small bags wrapped in tape.