Start with a rust penetrant
Rust penetrants contain a solvent to dissolve rust, a lubricant to reduce friction and a surface tension reducer to get deep penetration. “Home brews” like Coca-Cola, kerosene and mineral spirits don't have all those ingredients. Neither does WD-40 (it's a great lubricant, but it's not formulated as a rust penetrant). Those products simply don't work as well or as fast as actual rust penetrants (find penetrants like Liquid Wrench Penetrating Oil, Royal Purple Maxfilm and PB Blaster at home centers and auto parts stores).
Start by soaking all the bolts for at least 15 minutes before you attempt removal (Photo 1). If they still won't budge, move on to the “shocking” phase (Photo 2). You can smack the bolt heads with a hammer. But I get the best results with an air chisel and hammer bit (GRY No. CH117 hammer bit; from www.tooldiscounter.com).
I've also had good luck with an air chisel socket adapter (No. PH1050; from www.snapon.com). Slip an impact socket onto the adapter and pull the trigger (Photo 3).
If neither of those tricks works, heat and cool the bolt. The expansion and contraction will open cracks in the rust and allow the penetrant to work its magic. But before you apply heat, wash off all the rust penetrant (most penetrants are flammable). Next, remove any rubber or plastic parts that may be damaged by heat. Then heat the bolt head with a propane torch (Photo 4). Immediately shock the bolt with water spray (Photo 5). Once the bolt cools, reapply rust penetrant and try removing it.