Not everywhere we stay has a shower, or even water! We often can't carry enough water to drink, let alone shower at the end of every day.
So for that reason we like to carry around a packet of baby wipes which are great for cleaning yourself off after a days riding. They are wet, pre-soaped and don't require any water to use.
Two to four wipes are more than enough to get yourself quite clean and a packet of 20 is often less than $2.
Give it a go… you'll feel clean at the end of the day and your sleeping bag will thank you for it!