ideas of dishes/desserts that are make-ahead AND travel well
i see that you're in Philly. considering the brutal heat & humidity by you these days, and the fact that it may be sitting outside for a while once you get to the BBQ, for dessert i'd stick with a baked good that doesn't pose any serious concerns re: spoilage or melting.
blondies? brownies? biscotti? assortment of cookies?
How about a lemony couscous salad. With garbanzo beans, scallions and an assortment of vegies (some fresh corn, snap peas, celery or whatever appeals). Black olives could be included.
The dressing is lemon juice, lemon zest and some olive oil.
Easy to make. Served at room temp. Wouldn't need to be refrigerated for that distance.