[quote author=ApostlePaul link=1247407354/0#0 date=1247407354]I was wondering if there is a "best" way to tie the bag when using it as a liner on a canoe trip.[quote]
I've done the same basic method solotripper suggests.

I've used both a heavy duty twist tie (like some that a commercial laundry would use to tie together bundles of hangers) or extra-long/tick pipe cleaners to tie up the bag.  The twist-tie works better and doesn't tend break as frequently, but for a shorter duration trip the pipe cleaners would be fine.

You might want to consider something a bit larger than a compactor bag.  I've used a heavy-mil lawn bag for this.  It gives you extra length to twist the top and fold over before you tie-down.

Just keep in mind that your backpack will soak up water (and extra weight) and may very well remain wet for the duration of your trip (via both rain and sitting in the canoe bilge).

dd