Dirty Patches

I for one can rarely be bothered finding a towel/sink/other persons clothes with which to clean my hands - and crisp crumbs, among most other kinds of dirt, leave noticable marks over my shirts and trousers for which other people can tut at me and call me a hobo.
So sleeves should be made with a patch of material attached which looks the same as the material from the rest of the piece of clothing - but lift this patch and underneath is an absorbant material, good at collecting grime, water, etc on which to wipe your hands.
These could also be useful when, after washing your hands, you realise there is nothing on which to dry them.
The inside of the material flaps could be plain white material for making note of your inspired halfbaked ideas, lest you forget them within minutes - to be written on with with washable ink only.