Yep, onion paste if you can get it - or else onion powder. Can of tomatoes, or a few sachets of tomato paste reconstituted (not as good, but if space/weight is at a premium), garlic powder, ginger powder and some good commercial curry powder - and you are set for a pretty good base.
I'm a fan of using commercial curry powders on camping trips. Obviously not as good as what we are doing in the kitchen - but if you are hiking and lugging your own stuff around, it's a good solution. Fry the curry powder in the start, do a base as above and add garam masala at the end - you'll have something that might pleasantly surprise you.