"A towel is just about the most massively useful thing an interstellar hitchhiker can carry. Partly because it has great practical value...More importantly, a towel has immense psychological value." -- The Hitchiker's Guide to the Galaxy 

Your towel has many uses:

• If you wrap the towel around your shoulders and head, you can have advantage on any checks made against cold weather effects.
• You can use your towel as a bedroll.
• When you tie your towel to the mast of any ship, you can add your proficiency bonus to any check you make to control water vehicles, even in difficult terrain.
• When you wet your towel, you may use it as a weapon in melee combat causing 1d6 piercing damage on a successful hit.
• When you wrap the towel around your head you have resistance to poison damage, but during this time you have disadvantage on perception and investigation checks.
• If you swing the towel over your head, all creatures within a 60-ft radius notice you and pay attention to you.
• When you sling your towel over your shoulder, you can use your towel to gain advantage of charisma checks with other travelers and adventurers, as you are clearly a man to be reckoned with.
• After every long rest you may choose to roll a d100. If you roll a 42, you gain 7 luck points. If you roll any other number, nothing happens. You do not regain these luck points after they have been used. 
• One more absurdly random, towel-related ability you create with your GM that makes sense in your world setting...

Additionally please note that you can sit on your towel and enjoy a nice sandy beach in comfort and style, and of course you can always use your towel to dry off. "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."  -- The Hitchiker's Guide to the Galaxy 

Notes: Use after a good bathing twice.