Another one to cross of my to-do list - car seat strap covers. Something very functional and needed since the dog decided to chew into one of the covers a long time ago. They're basically like making potholders - four potholders (you know, two for each kid). Here are a couple fun tutorials of similar strap covers here and here. (do keep in mind if you decide to make some, to make sure they don't interfere with the other fuctioning parts of your child's particular car seat)
And while were on the topic of strap covers, figured I might as well show a really quick one I made last year for our bike trailer. I just took long strips of fleece (about double the width of the strap plus about an inch seam allowance/wiggle room) and sewed them into tubes. Don't bother turning the tubes right side out, fleece doesn't fray. The best part is that you can adjust the strap length by just scrunching down the fleece.
happy biking!