Concentrated Yerba Mate
You could do that, but it would not save much weight and will be perishable.  The concentrate will have enough water to spoil.  If you want to take this course still, prepare a concentrate by using about 4x as much mate and steeping somewhat longer.  You can reduce it over low heat, but probably not enough to get a sludge without hurting the flavor.

If you're concerned about weight, I suggest light equipment. 50g of mate will make you about 15+ cups of it.  To steep it, I suggest getting a very light tea infuser, either a basic basket or cup with built-in infuser. This way you can enjoy fresh yerba mate.