regarding Baltimore: it's not as bad as it used to be but it isn't the best place to get lost. If you have difficulty getting around, do yourself a favor, and go into a bar/pub/restaurant and ask them to call you a cab. Baltimore has a few very nice areas, but those areas aren't very big at all and are right next to some of the tougher parts. Philly is similar but the nicer areas are bigger and around the tourist destinations.
In Baltimore, get some crabs. Same holds true for Washington, but there are so many great foods in that city... and it obviously has international influence. I'd get shelled but crabcakes are a good choice. Also, their Little Italy is pretty friggin good too.
Nothing is more American than a hotdog so grab a couple chili dogs at Ben's Chili Bowl as that place is an institution. Ray's Hell Burger (VA, but off the Blue/Orange line one stop out from DC) is the best burger joint around in is quite famous now that Obama made it a point to eat and bee seen there. i don't know what you're budget it, but there's this restaurant in Georgetown called 1789... to restaurants change all the time in DC but that place is a staple and has a Revolutionary War feel to it... I usually take out-of-towners there. More expensive, but if you want one good meal I'd recommend that.
In Philly a cheesesteaks are famous and the two most famous places for that are Geno's and Pat's. I'd say Geno's is considered better by my friends, but Pat's isn't bad... Jim's Steaks is personally where I go to get a steak with Provolone. For all other UKers, Jim's is fairly easy to get to from 95. So, if you have time and decide to take the long way on 95, it's a quick stop and definitely worth it.