This may be a dumb question but what the hell. So after my last trip I seemed to have lost my sleeping bag stuff sack. Its a Marmot Sawtooth 15 degree down bag and looking around the internet I found out that the stuff sack volume was 11.6 liters.

Can I just buy any old stuff sack with approximately the same volume and put it in there?

Should I spend the money on one of those sea to summit dry sack compressions things?

Should I get one at least 12L or could I go smaller?