Books are the most common media for magic. The portability and ease of stacking spells (and volumes) makes them ideal for many, but there are countless variations. For instance, reptilian witches often carve glyphs into their scales.
Forest sprites on long journeys stuff pouches with painted leaves. The magic lasts until the leaves dry out or are eaten.
Magic users with a technology background sometimes use USB sticks charged with enchantments, often programmed to convert electricity into spell energy.
In areas where magic need be hidden, pencils work surprisingly well and are favored by pixies in human form. Pens tend to explode due to an inherent conflict between magical spells and mundane ink.
Kraken, lacking hands but being spoiled with tentacles, use a water jet-based technique. Spells are imbued into currents of water exhaled from their bodies that are then gathered up and woven together by their tentacles, and kept orbiting around the creature until they are called upon for use. This method is often used to duplicate and share spells amongst the leviathans.
Sentient deserts work the wind to carve elaborate glyphs into sand dunes, often to trap or protect creatures slumbering within.