How long do peanut butter sandwiches last at room temperature?
I've done it before without problems.  Even if they're peanut butter &amp; jelly (something that's typically stored in the fridge), it has so much sugar in it that it's inhospitable to microbes.

If you want to play it extra safe, and the sandiwiches won't be easten shortly after you leave, you could place them in the freezer and then let them thaw in your bag.

... all that being said, if you're in the US, the TSA considers peanut butter to be a gel, so won't let you fly with a container of it.  I have no idea what their rules are in sandwich form.  (I've never tried it, as I typically fly w/ cold cut sandwiches, and just take them straight from the fridge before I go).

update from Erica : "I have flown with peanut butter sandwiches in our carryons. New TSA rules mean pulling it out of bags to send through the scanners, but they had no objections."