I get parents to provide "specialty" food, such as jarred baby food and formula, or anything specific to a dietary need (ie; no/low gluten products).
I would rather that they make the bottles and pack a certain amount. I would ask for the usual number of daily bottles, plus at least one. I don't want to be fussing with mixing formula. Plus that stuff isn't cheap, so I don't want to ask parents every week or two to be bringing more. Then they start wondering if I am preparing it properly, using too much or too little, etc.
And I agree with playfelt about the bottle vs cup idea. If your child is still drinking from a bottle, you supply it and it's contents. Since I really only care for kids around 1 and up, I will supply cups and what goes into them.