I use a skidless yoga towels, some of mine have the silicone bubbles some without.
Depending on the studio I may keep it rolled up for start of the practice and then as sweat starts rolling I roll it out.
I have seen other folks spray their towel at the start of the practice for a bit more grip from the get-go.
I use them when I choose to run to a local studio rather than carry a heavy mat or if I need a barrier to public studio mats.
I also keep one without bubbles in the car so I basically have a towel wherever I go.
More importantly, a towel has immense psychological value... any man who can hitch the length and breadth of the galaxy, rough it, slum it, struggle against terrible odds, win through, and still knows where his towel is is clearly a man to be reckoned with."