I've used Crocs for years but am trying a pair of Under Armour soccer slides that are quite a bit lighter. They work in bare feet or with socks; I sized up for comfort. They crush flatter than crocs--easier for side pockets.
I am away from camera and scale so don't have weight or pics for you yet. They have worked perfectly this season. Cabella's, Sportsman's Warehouse, The Soccer Shop, etc.
For ultra-light I am going to try a pair of hospital booties. They won't hold up to heavy use but will work to keep dirt and sap off easily. (Even doubled up they weigh less than one sock.) And they may work for fire starter... Will break out the BBQ bucket to test this weekend.
Any brand of slide would work. This is UA's URL for pics.
(Disclaimer: I am not now, have never been, nor ever expect to be associated with any company that would benefit from this insightful, informative, and yes... even sensitive endorsement.)