Spare batteries for your GPS
Just a note for anyone who uses a handheld GPS powered my AA batteries. NiMh cells are simply awful for self discharging, so unless you top the things up shortly before flying they won't be near 100% capacity.
However, Sanyo have for a while been selling their Eneloop cells, which really don't self discharge. I have around 24 of these that use in my camera/flash rig, and they are simply fantastic. They have been left for several days fully charged, and didn't loose any charge at all. I have actually left one of these cells for 2 months as a test and again it only took a handful of mAhrs to top it off. Almost as good as LiPo or LiIon.
Don't risk using standard NiMh cells - especially higher capacity ones, as it is the higher capacity cells, generally, that have the worst self discharge characteristic.
Sorry to sound like a shareholder, but these things have saved my bacon so many times.