Coffee is a really bad idea.

It sucks out hydration from your body + in sunny regions it's currently very hot, so you need additional hydration, not less.

Additionally, if that wasn't bad enough, caffeine increases your sweating & may make you feel hotter.

It's also a very US-American culture thing, that someone is looking for substances rather than psychology & willpower tools, to accomplish a mission.

You can feel less hunger with the right mind, than with an average idiot's mind & coffee. :)