Pretty sure most cops get trained on common hiding spots (mostly for drugs). If they're doing a thorough search they'll probably find your stuff, then you'll be viewed with more suspicion because you knowingly hid it.
That's not to say you can't store a memory card in a legitimate but not overly obvious place, like an obscure pocket of a bag or slipped inside a first aid kit or something. Swap cards if you have a chance, then if the other one is found, well, gosh, it got full or had an error and you just now switched to your spare.
If you somehow need to bring "special" items that would cause more trouble, make a special trip with them and be prepared to drop/stash them on-site if something comes up. It sucks to drop a $30 set of picks, but it beats a $100 ticket (and you benefit people like me, who found picks that someone else dropped
). In general I try not to explore with anything ridiculously incriminating, but as others have said, pretty much anything can be a "burglary tool" if the cop wants to be a dick about it.