A smallish towel (about 100 x 50 cm / 39" x 20"), Czech army surplus. These have not seen any private parts and sweat - they are unissued.
Note! 24.5.2019 The latest batch was single-colour and in a NOS condition. The situation has changed from time to time and here's where we are now.
Admittedly, a large towel is better overall, but when travelling, it's better not to waste precious space. This is where a smaller one shines! In addition, the price is next to nothing, so why not buy a bunch of these anyway? Keep in mind that, according to a certain venerable tome, a towel is the single most important item a traveller can carry with him when leaving home.
Apart from some storage dust or occasional old stains, these are as new.