Wilderness Concepts

I'm planning several kayak camping adventures this summer, from overnight to about 4-5 days. There will be some portaging involved, and I saw somewhere how an external frame backpack can be utilized cleverly to portage a kayak above your head with minimal strain to shoulders and back. But I'm wondering how cumbersome such a backpack would be to stash inside the kayak while paddling. I'll be padding to different locations each day, so don't have the option of just leaving it behind at camp for the day. I'll be solo mostly, so need to make sure I'm planning for the most efficient way to travel & pack. Should I consider buying an external frame backpack? Suggestions?