At the very least you'll want enough tools to fix a flat and carry out basic repairs/adjustments to your bike.

Depending on the type and age of the bike you get you may only need a folding hex key/screwdriver tool which will pretty well fit any fastener on the bike, chain tool and spoke wrench. For flats you'll need a spare tube(s), patch kit, tire levers and a pump. Other bikes may require more tools such as various size wrenches (spanners).

Some spares, such as tubes and spokes would also be a good idea. Most people also carry such things as duct tape, first aid kit, cable ties on a regular basis, not just for touring.

From there the list goes on depending on what type of country your travelling through, if you're camping and cooking, or staying elsewhere, climate at that time of the year, and personal equipment.