It's amazing how few tools you really need to make an altered book. You can get by with only a glue stick, a cutting tool such as a box cutter and a pair of scissors. Actually, you can do an entire altered book with only folding. Or, only cutting. Or only a pen or crayon for writing or drawing.
But, most of us use many art techniques in our books. Here is my list of basic AB tools.
Box Cutter and small pliers to snap off tips to bring up a new tip. (you might prefer Xacto knife)
Cutting pad, the self-sealing type.
Golden's Acrylic Gel Medium.
Ruler with metal straight edge.
Credit card (no, not for buying supplies, silly! It's for smearing and spreading gel medium and paints, and also for use with clamps so you don't mar your pages.)
Pencil and pen.
Small spray bottle with water. Use to help keep sponge brush damp, and to do quick clean ups.
Deli wrap paper or wax paper.
Dorland's wax to wax over pages, particularly if there is a stickyness problem.
Stencils of letters and numbers.
Rubber stamps (I use them for text).
Ink pad with permanent ink.
Post it notes. Tuck them in to help plan where you will use an image or quote.
Clamps for holding sections together while glueing or cutting.
ICE (Imagination,Creativity, and Enthusiasm)
If you have additional things you can't live without in your tool kits, please post in the comments so you can share what you know. We all have favorites!