What the heck does “You can’t have your bread and eat it too” mean. Cuz I’m pretty sure that when I buy that cheap $0.99 bread I make a sandwich with it and eat it

It is a proverbial saying that means that it is not possible to have or get everything one wishes for in life and that one must make choices.

Explanation:

The phrase "you can't have your bread and eat it too" is a metaphorical proverb that suggests that you cannot have the best of both worlds. It is not to be taken literally and is used as a proverbial saying that is directed at someone or anyone for that matter, who wants everything or wants to get everything.

This saying is generally used when there are conflicting interests like for example, someone wants to work less but be paid more. In this case, you can't have everything you wish for. If you work less, then obviously the pay will also be less. But if you want more pay, then do more work. This presents a dilemma of choosing between two things, foregoing one over the other.

the atm that sounds like it should be the answer

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there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.