Keep drinks and liquids away from books and library materials. They can cause damage on contact. Resulting damage is permanent. In addition, coated papers (the finish is often glossy) will stick together if they have been wet and are allowed to dry without special steps being taken.
Avoid eating over library materials so that they don't become littered with crumbs. Notice what appears to be breakfast cereal on the book below.
In addition, food on the hands can transfer onto books and paper. An extreme example is shown below. Food and food residues also attract pests.
Be vigilant in regards to liquids! One spill can cause damage that is difficult to repair. Often, such materials need to be replaced.