My university is making a big effort to be green, so we have a neat policy at our on-campus coffee house, pi cafe, that if you bring your own receptacle you get a discount on your drink.
Being poor college students, we never seem to have any travel mugs with matching tops with which to obtain this discount, so we use jars. Jars are really poor at insulation, though... and thus the pi cafe heat sleeve was conceived. (It also works on regular coffee cups, of course).
It goes like this:
Cast on 34 stitches with worsted weight or similar yarn. I used size 8 needles, but 7s would be fine I think.
1x1 rib for 5 rows
K next row
where blank space is K in main color, filled in is K with contrasting color.
1x1 for 5 rows after chart completion.
Turn inside out and stitch ends together.