You may use any pattern you like as long as the finished dimensions do not exceed 36 inches by 48 inches and there is no fringe or other adornments along the edges.
If you do not like to take on large projects such as afghans, you may knit or crochet 6 X 6 inch squares or 12 X 48 inch strips. It would take 48 squares or 3 strips to make a lapghan.
The lapghans may also be made of fabric, so sewers and quilters are welcome to volunteer as well.
(Click on title of pattern to open pdf version)
Crochet in the Car (This website includes multiple handbooks and patterns for crocheting from beginner to advanced levels.)