One thing I've discovered is that like drinking even when your not thirsty keeps you properly hydrated, snacking while you paddle keeps your blood sugar up and along with staying hydrated, keeps you physically and mentally alert, very important when your solo.

I keep a zip-lock bag full of trail mix, heavy on the dried fruits and nuts.
Dried fruit gives you that slow release of natural sugar that keeps your blood sugar from spiking and then crashing. I nibble often as I paddle and while portaging.

Hitting the water early, and getting the majority of your miles in early before the wind picks up will go along way toward having a good days paddle without burning yourself out. I'm not shy about taking a quick cat nap at lunch after a brisk morning paddle, does wonders for your energy level.

Unless your paddling to stay in shape, the first few days will be a strain on you, fit or not. Taking a layover day before you burn yourself out or injure yourself pressing to hard is a prudent idea.

No-one is counting how many trips it takes to cross a portage or how much you can carry. The idea is to have fun, enjoy your trip and challenge yourself enough to keep it interesting without doing something stupid ;)