An easy way to maximise your yarn usage, if you’re trying to use up stash, is to combine two different yarns into one item. The easiest way to do this is with stripes. If you don’t quite have enough for the item with just one of your yarns, pair it with another to get the total required yardage.
Stripes work best with simple stockinette based patterns, as they really show off the colours without getting lost in lace or cables.
You can also work with garter stitch, such as this short row shawl which combined two handspun yarns that didn’t have enough yaradage on their own to make much, resulting in a good-sized crescent shawl.
If you are looking to maximise your yarn usage by using stripes, try to make sure that your two chosen colours have a good contrast between them so that the stripes really stand out well. Also make sure that your yarns are the same weight (fingering, dk, aran, etc.) and if making a garment to be worn have similar fibre contents so that they will work up together at the same gauge and won’t distort with wear (a cotton yarn may stretch more than a wool yarn, so unless you want stretched out stripes stick to just the one fibre type).