@HansonBro did a good job but ill try to add on to it. Ill try to think outside the box.
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Those ramps you can pull up on are incredibly convenient for getting under a car
- A creeper to lay on while you roll under the vehicle
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Ultra bright flashlight
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Bluetooth OBD2 adapter. They can be found for $20-30, I think I paid less than $15 for mine years ago and I still use it all the time. There are a million different apps that you can download on your phone that will pull codes for free
- I have been working on cars my entire life, and I have never used gloves until the last few years. I only use them when things are really messy, but disposable heavy duty nitrile mechanics gloves are really nice to have sometimes
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Typical garage chemicals like penetrating oil, brake cleaner (can be used for dissolving grease and oil off parts but sometimes it can remove protective films off certain parts and cause unnecessary corrosion, in those cases carb cleaner is a good alternative), a variety of greases and lubricants, anti-sieze, thread lock, and keeping a bottle of each automotive fluid for the specific vehicles you own (power steering, brake, coolant, oil, transmission)
- A variety of hose clamps and zip ties
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Flexible magnetic pick up tool for when you inevitably drop a nut, screw, or bolt in a hard to reach place
- Battery charger
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U-Joint adapter for your sockets for hard to reach areas. I have had to use mine so many times over the years
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A set of torx bits
- Utility cart
- A torque wrench is a good idea. There are proper specs that pretty much everything needs to be tightened to. For people with experience working on cars, we can usually ballpark it close enough for there to be no problem without a torque wrench, but it wouldn't be a bad idea for someone without the experience.
And the most underrated tool of them all - An extra set of hands in the house that can help out in a pinch if needed. My dad owned a lot of classic cars and did all his own work on them, I couldn't tell you how many times as a kid my dad would call me to the garage to help him out for a minute just because some things are a thousand times easier with an extra set of hands.
Not all of those are must haves, but they make working on cars a lot easier. I bolded what I think would be the most useful.