A. H hit the nail on the head. I loved the fact that my mom could be the "bad guy", and she didn't mind playing the part, either! Sometimes it'd be pizza, or popcorn and coke, other times it'd be that velveeta/rotel cheese dip and/or veggie snacks. If it's a holiday themed movie, obviously some hotchocolate and peppermint flavored snacks. My mom somehow mastered the art of being a hostess that would kinda surprise us with some treat, and keep an eye on what was said/done (mom's BIGGEST no-no was making fun of someone especially if they weren't there to defend themselves), but didn't "hover" so much. 13 year olds like their independence and want to be "cool" but they are still children and dig the treats and security. There's no pressure on these "predates" if you know your mom is there so it automatically cuts out things you might be nervous to do, ya know? Being able to have a relationship/trust with my mom where my friends felt comfortable enough to come over and we could have fun, but the security of boundaries, actually helped build the relationship and trust for later!
I think the OVERLY girly movies like Princess Bride aren't too good a choice because you're dealing with 13 year old boys who aren't going to enjoy that at all. I went to see Ever After b/c it looked good on the previews, but OMG girly....the best part of the night was hanging out afterwards and watching the males that were dragged there on dates LIMP out like they'd been castrated! Like previously mentioned, the Bourne movies are pretty great choices. Comedies are good, but these days you really need to check them out first for content. One of the first posts you received had a site that shows you parent's reviews: that could be a great tool. I also think that PG 13 movies are fine if you read to see WHY they got the rating. Some are sexual inuendo which might not be the best choice for a "predate" but if it's just action or "some language" then honestly, they'll hear worse at school!!!
Kudos to you for being inconvenienced for the sake of your daughter, for opening up your home so you can know what she's up to, what her friends are like, and steer the direction of the evening.