I use balsa strops most of the time with black and white compounds and a little bit of oil during application as they are very hard and waxy, i really like the results, the feedback, the ease of maintenance and the dirt cheap cost.
Im not into mirror edges and ultra high grit anymore but i still got some loaded strops with 6-3-1 diapaste and 0.5 wicked edge paste which i store in ziploc bags to avoid contamination. i rarely use them anymore, too much a hassle, rather pricy and not so happy with the speed and results compared to my bread n' butter white compound.
If you are really obessed with contamination, dont forget the plenty hard carbide clusters accumulating on your strops after a couple of uses... The only way to avoid that is a single use strop...
To be honest my everyday strops arent in a ziploc and they arent very clean yet i can get a hair whittling edge out of them.