Depends on what you install.
I install everything from fixtures to graphics. My installation kit that goes everywhere with me has a small socket set, screwdriver set with assorted bits, allen wrenchs, and at least 2 of every installation tools I use on a daily basis plus a wide selection of squeegees and scrapers.
I have a spare tool/hardware box that lives in the truck with a wide assortment of hardware like; assorted screws, anchors, drop ceiling hooks, aircraft cable and ferrules, pop rivets, bolts, VHB, and glues along with a few tools to install said hardware. I also save extra hardware from previous jobs here too. It's been a life saver on more that one occasions and saved countless trips to the hardware store.
I broke down and bought the
Ridgid Pro Gear Cart and 2 each of the small and medium size tool boxes. Now I have a modular system at a reasonable price. It is easy to mix and match quickly based on the type of job. My basic installation kit lives in two of them and in the back seat 90% of the time.
I always carry a 4' and 2' level, a 5' ruler, and a laser level under my back seat.
Center console has a squeegee, air release tool, stabilo , pens, small crescent wrench, and a tape measure. They come in handy but it's not so much planned as collect there, and I have to redistribute them occasionally.