MT,
And others are right about getting an early jump on the day, and the wisdom of 2x portaging.

Your still a young dog, early 30's by your bio.
Assuming your in great shape, you have 2x choices the way I see it.
You can travel light, like some here do, without any camp comforts or special meals, or 2x portage and enjoy yourself a little more ;)

I don't know what your route is, or the degree of difficulty of the portages along the way. I do know that I've seen plenty of single portagers of all ages, either taking breaks half-way across tough portages, or coming into the end, so exhausted they needed a break to re-coup before paddling on.

I 2x portage, and my rest period is my walk back. I almost never stop on portage under load, as I'm light enough going 2x, that it's not exhausting for me.

Factor in the risk of falling/hurting you back under full load, and the loss of the " woods" time on the trip back, I'd say unless your a road runner and need/want the high mileage, you better off 2x tripping in most scenarios.

Someone here posted once about the time differential between 2x portaging without a break, and 1x under a good load. Seems to me the difference was so little and benefits so much better 2x portaging, it wasn't worth it, unless your going for the gusto everyday.