I bought myself a camelbak transformer this year. I didn't need a military pack specifically but ran across it somewhere and liked the removeable pouches. So I take just the basic pack when biking which has a small sipper pocket at the bottom where I put a basic PSK. Then if we hike or travel I add on the other one or two pockets.
Wife thought it was silly at first then decided she wanted one so we got her one and my son the skeeter.
Both kids have mini-mule's ar wrapped for Christmas now.