I hate to say it but WalMart/SAMS Club has some of the best "gorp" (have to remember that) I've had, and it comes in BIG bags, few different flavor combos.
+1 on the Pop Tarts - lots of calories and they're fortified. Don't forget Granola though that tends to get stale too quickly (recently opened a box of Quacker 100% Natural - 100% yuck).

"Gosh, you have a lot of nice toys here." - Roy Batty