I've got two,
1). Mr. Heater portable Cooker/Heater that runs off of small propane bottles. I found that it really throws out the heat inside of a flip over blind. If you're not using it for heat, it warms the coffee really nice too. On the average, a small bottle of propane last about 4-5 hours of steady use. It is also small enough to fit completely in the gun box. Fleet Farm has them for about $39.00
2). Lucky Duck, AA battery operated spinning decoy. This is a full sized decoy vs "baby decoys." On the average, I got about 6-hours of continuous use on the 4-batteries. It came with a two piece metal stake mounting system. Fleet Farm had them for about $40.00