1. They want to have many of something such as food or money.

2. They want to have more of something such as food or money.

(Which one is correct? Do we have to use 'more' or' many' in this case?)

More is the better of the two.

Thank you for your help.

What about the follwoing?

3. They want to have much of something such as food or money.

(Can we use 'much'?)

More makes "more" sense.

In this case, the second sentence is correct: "They want to have more of something such as food or money."

The reason is that when we are talking about quantities or amounts of something, we generally use "more" instead of "many". We use "more" to compare amounts or quantities and indicate an increase or a desire for a larger amount. On the other hand, we use "many" to indicate a large number of countable objects or things, but not when we are talking about quantities or amounts.

For example:
- "They want to have more money." (correct usage)
- "They want to have many money." (incorrect usage)

Similarly, we can say:
- "They want to have more food." (correct usage)
- "They want to have many food." (incorrect usage)

So, in this case, to express a desire for a larger amount of something like food or money, we use "more".