This might sound stupid, but be very careful with rechargeable batteries. They can deliver a large current on a very low impedance resulting in high temperatures. That's the reason why Nikon batteries are provided with a cap to transport them. If you change batteries and forgot the protection caps, be very careful and but them in a plastic bag to pack them individually before putting them back in your bag.
I have had a (very) bad experience just by carrying a battery pack for my D200 grip (consisting of 6 AA batteries). I had the pack in my pocket together with a keyring and a few coins. After a few minutes, I smelled something burning until I realized my pants were on fire... This is not a joke... here is a picture with the result. By the way, everything is still working and I am ok but this could have been worse.