Is there anything worth eating on I-81 in PA?
Look up Scranton, Camp Hill/Mechanicsburg/Carlisle, if you're looking for sitdown joints. Seriously, you're heading straight through a bunch of places with tons of people (unlike I-80).
But, heck, you're passing through some really beautiful country. I'd suggest pulling off at a state park, and enjoying a local sammich (Lebanon bologna on Martin's potato bread, personally, along with some Grandma Utz chips). Great places to stretch your legs and relax a bit on a long drive.
"Old Forge" Pizza is a speciality in the Wilkes-Barre / Scranton area that people either love or hate. (Old Forge is a community between the two cities where, I guess, it began.) I'm partial to Pizza L'Oven, which has locations in and around W-B; unfortunately, I don't think they open until 5:00 PM. It's a thick bread crust pizza, heavy with oil, so the bottom virtually fries up and is very crisp. The sauce (a sweet red) is applied very sparingly; the better ones, IMO, are very chunky. Then there's cheese on top. As for toppings, choices are (1) onions, (2) no-onions. Kind of minimalist heaven ... Orders are by the piece, not the pie, and are cut into rectangles about 2" X 4". (You can sometimes order by the tray, but the menu will specify how many pieces per tray.) Others still in W-B and / or more familiar with the topic can, I hope, offer some lunch suggestions. Discussion about favorite locations can get pretty heated ...