I don't believe there is a way to sell them, however they are still worth having anyway. You use 5 of each potion on a pack, so it goes by fast. I'm mostly F2P as well, and have a second fully F2p Account. Soon there will be a general sale too, where you can get packs for even cheaper than they are now, so maybe down the road you will be able to save some DEC or such to buy a few. I didn't think I'd get any before the general sale but I've opened 6 or 7 already. Maybe someday they will have more use.