On my trips I take fresh potatoes, sweet potatoes and onions as well as other fresh produce.  I like to boil sweet potato slices with ginger, then fry in olive oil with sliced potatoes and onions .. this is very strengthening.   I’ve gone on trips lasting from six weeks to 10 weeks with lots of portaging, and don’t mind carrying the extra weight of the produce over the portage as the taste and nutrition are well worth a little extra effort.