I know it doesn't look as pleasing, but you can save weight and space by putting all your dry goods (spices, tooth powder, seeds, rice, biscuits, vitamins, powdered milk and protein powders) in plastic bags. Wet goods (oils, sauces) go in tins or metal/glass/silicon containers if you're being diligent. "BPA free" labels on food storage doesn't mean the plastic they use won't leech into your food from agitation, sun and body heat, "BPA free" is just an advertising technique and means they swapped the compound for another xenoestrogen.
Plus if you keep dry goods in plastic bags, you can blow into them and inflate to provide padding - this is perfect for sandwiches to stop them getting crushed.
Also don't bring your own packets of salt or pepper unless you like Himalayan fancy salt- it's much easier to nick a handful of paper sachets from a cafe or restaurant, et voila, easily sourced, decently sized portions available everywhere, plus you can burn the paper when you're done. Same with sugar and sauces and, within limits, those small milk sachets for drinks (bring powdered milk if you want milky cereal).
