I've used shock cord, 1" fold-over elastic, and 3/4" non-roll elastic. The shock cord was hard to sew through and finish. I intended to use the 1" fold-over as the finished edge of a pocket but it was difficult to stretch it and sew simultaneously. I ended up just running it through a sleeve. It tends to fold and 'roll' inside the sleeve but does hold the pocket opening snug. The 3/4" non-roll is the best I've used so far: easy to sew through, requires a relatively small sleeve, resists rolling, and holds well.
On the other hand, the elastic in the MLD pack pictured above appears to be much smaller than 3/4", so perhaps that's all you need.