It greatly depends on if you have an access to refrigeration facilities
and if you keep chalav yisrael/if you trust chalav akum of destination.
On the other hand, it's a bit easier if you don't hold strictly to bishul akum
and can ask the hotel to do the "baked-kosher-fish-with-skins-on-in-a-
double-wraped-foil method".
Most hotels I know would not serve something you bring from outside,
unless it's from a caterer they trust/use.
Also it may not be practical to bring crockpot/sandwich makers etc.
I'm assuming a more restricted case without access to fridge, (but
small kettle/emersion heater), no local processed/packaged kosher
food supply, no supermarkets nearby.
Tinned fish (tuna, salmon, sardines), vegetables (sweetcorn, beans),
vacuum-packed vegetables (mini potatoes, beetroots) dunno if they still
make it or not but hummous in ambient package (the one you add water).
Couscous. Instant soup/noodle soup, "Lebrioyot" ambient meals with
internal heating source. Dry cereals, fruits for snacks/breakfast.
Baked goods (pastry, bagels) would last a few days without refrigeration.
I can easily last 1 week with the above and occasional supplements of
fruit platters.