You think a grinder is useful... Get yourself an oscillating multi tool. There was a point in my life where I had a lathe but not oscillating multi tool. Never again....
My top 3 must haves:
Impact Drill
Sawzall
Oscillating Multi Tool
Two thumbs up on the OMT. Can't remember what I needed to do 10/15 years ago but along the lines of trimming the bottom of installed door trim/cut a bolt flush and a friend told me Harbor Freight had something called an "Oscillating Multi Tools" on sale. Never heard of it but that saw blade set up is amazing and the pointed sander handy too. Specialty tool for sure but when you need it, will do what no other can.
Had a chorded drill (with key) forever but springing for a battery pack around 05 was a hassle reducing game changer.
My number one "how did I live without this?!" was my first rechargeable B&D electric screwdriver. Moved into a new house around 92 and needed to do all of the shades/shelves, etc. stuff and finally bought one. Had done it the old fashion way in my previous 2 houses. Very high on my greatest inventions since sliced bread list.