Why are "de quoi" and "du manger" used here?

Question

Il fait sacrément froid aujourd'hui, vous ne trouvez pas ? Heureusement, nous avons prévu de quoi vous réchauffer ! Pour ce qui est du manger, je vais vous demander de patienter un peu.

1. Translation : "We have prepared something to warm you up"

Why is "de quoi" used here? Is it wrong to say instead:

Nous avons prévu ce qui vous réchauffe !

2. Translation : "As for what to eat"

Why is "du manger" used here? Is it wrong to say instead:

Pour ce qui est de manger,

By the way, do you need to use the infinitive form "réchauffer" after the phrase "de quoi"?

Answer 1

Du manger here is a somewhat elevated formulation where they are using the nominalized form of this infinitive (only a few infinitives can be used that way), which means "food". Usually it's used with implications about the pleasures of eating or in the set expression le boire et le manger, i.e. "drinks and food" (perdre le boire et le manger: to be obsessed with something to the point of forgetting about eating or drinking).

Answer 2

"De quoi" is translation of "things"

For example: "J'ai de quoi faire" = "I have things to do"

You can say "Nous avons prévu ce qui peut vous réchauffer", but meaning is a little different : "We have prepared things that can warm you up"

Phonetically, your proposition sounds like "Nous avons prévu ceux qui vous réchauffent" = "We have prepared those that warm you up" and this make the sentence really strange, but "Nous avons prévu ce qui vous réchauffe" can be a sort of french but is not used at all.

"Pour ce qui est du manger" = "As for what to eat" or "And about the food" more exactly, but in this context, you're right, "Pour ce qui est de manger" is french and stands for "And about eating" <- I don't know if this is really english.

To know if you write "réchauffer" or "réchauffé", some french people like me replace the verb by the verb "Prendre" because it directly sounds right or wrong : "j'ai prévu de quoi vous prendre" is french, "j'ai prévu de quoi vous pris" isn't infinitive but past participle, and is not french too.