There is always something to do, so my tool bag always comes with me on all jobs as well as all around the house. It is cost effective and saves you time too.
Start with a tape measure the metal kind, Ikea have a great one at about $1.29 US (slightly more in Canada). A hammer, pliers, utility knife with blades, I like Stanley as it never slips. A cordless drill with bits is great as there is always one screw that does not want to come out. Palette knife, a ratchet screwdriver, a set of allen keys plus add some work gloves, safety glasses, sandpaper, glue, duct tape, selection of screws and nails packed up in an old tote bag or study box and you are good to go. Add other items as you need to.
Now you can tackle putting together flat pack furniture, hanging pictures and an assortment of small repair jobs without spending a fortune.