If your traveling for 18-24 months where do you fly into and out of in the states, where do you go after the US? That will determine a lot of your route?
I read it to mean in 18-24 months, not for 18-24 months.
Almost any consumable object--toiletries and such will cost less in the US.
I think prices are very similar, by the time you convert the currency, add tax, and so on. But supermarket food is cheap in the US - from raw ingredients through frozen meals and store-made read- to-eat meals. Between those plus beer | wine bought in the supermarket, day-to-day expenses can be cheap indeed.
Going out for meals and drinks isn't as cheap as here, and we do it rarely. Occasionally to a Mexican cantina - because we like the food. But even that can be nicely bought in a supermarket (frozen or fresh). We avoid almost all things that pass for regular "food" in the US ... unless your tastes run to fried, fat, sugar, and starch. So no pizza, hamburgers, fries, waffles, pancakes, and so on.
As soon as we rent our car we go to the first cheap supermarket and stock up ... we also buy a cheap Esky (or sometimes take a collapsible one from here) and get a cardboard carton or two to store dry goods. A couple of plastic bottles we freeze every night as our "ice".
We also take good quality and lightweight plastic crockery + cutlery, glassware, some lidded containers for leftovers, and even a nice tablecloth ... we do lots of picnics!
