Thank you for the comment, I'm glad you had fun. :)
There's no drink planned (yet) and it might not be relevant in the game. The combo is supposed to be burger + fries with regard to the skit. But I did give some thought into what drinks Sammy could be selling. What I've come up with:
1. Cocaine Cola (on what the protagonist may OD on)
2. Sixfold/666-fold espresso (an over-caffeinated drink)
3. Pepsi
I especially like the "Pepsi" option, especially with regards to other choices, because (just like her menu and maybe other things in the game) it may seem so simple and silly but it works in so many different aspects...