There's an ingredient in many commercial hair-styling products that straight hair (or any hair, for that matter) can do without: alcohol. It's often found in large amounts in some of the cheaper stuff, and it strips off the oils your hair needs to look rich and healthy. Alcohol makes hair -- especially straight, fine hair -- look dry and lifeless.
So look at ingredient lists on any gels, mousses, leave-ins or spritzes. If alcohol is one of the first three ingredients, leave it on the shelf. If it's farther down on the list, that's fine. You needn't worry about a tiny amount.
If your hair is exceptionally dry, you may want to invest in alcohol-free hair products. They're out there.
Finally, to give straight hair some full-time depth.