For the most part, when it comes to regains, characters will get what they ask for. However, the vending machine's capricious nature is well-known, so sometimes it may give you a regain you weren't expecting! So even if your character wouldn't ask for it, it's perfectly fine to request something you'd like to give them. This also allows you to give them something else instead of what they've asked for, in the event that you don't want them to regain a particular object!