So recently I've been biking with external frame hiking backpacks. I use a Jansport hiking bag and an REI day pack. Has anyone else tried doing this? I usually gravitate towards bags with a high Liter count and these bags do the trick. A lot of descent biking packs are pretty expensive, but I can find hiking packs at rummage sales for less than $15 and they work just as well, maybe better. What are your thoughts on this?