forget the usual hand tools. With $100 to spend, what tools would you suggest folks to get which might not be used all of the time but are very handy to have

I'll start with some obvious ones from harbor freight and am focused on low cost because these are for the occasional user and we're looking for simple funtionality

7 Function Digital Multimeter
Cen-Tech
Item #:69096

Price:
$4.99

18" Telescoping Magnet
Item #:37187
Price:
$2.99

Telescoping Mirror
Central Forge
Item #:7361
Price:
$3.99

One Person Brake Bleeder Kit
Item #:37201
Price:
$4.99

18" Long Neck Black Funnel
Item #:66479
Price:
$1.99

Fluid Siphon Pump
Item #:93290
Price:
$5.99

Grease Gun with Pistol Grip
Central Pneumatic
Item #:66664
Price:
$8.00

$14.28 for vacuum gauge

subtotal $47


$25 for compression tester

subtotal $72


$30 oil pressure tester for metric and SAE

OK, I went to $102

for $100 (OK, $102) you will find the above items invaluable and a vacuum gauge is nice to have when making a quick inspection of a used car.

 

This is a tuff topic because so much of it relys on what the person already has. I like the list you made they all seem like good buys. I am not a big fan of the grease gun, sure its a great price but for most hobbiest the a small manual one is fine. I have had one of these small ones for a few years I think I am still on the first tube.

Grease Gun with 3 Oz. Grease

Bore scopes come in very handy, even on house hold jobs. I paid around $30 for mine with a case. They work great. Of course you need a laptop or something with a USB.
USB Borescope Endoscope Inspection Snake Video Camera Computer Home Inspection | eBay



I paid $26 for this one with a coupon. They are great for check coolant (heat) flow on a car that is over heating. You can check thermostate operations in minutes They can help track down a miss or a lean condition by checking the heat levels on your exhaust manifold.
Non-Contact Infrared Laser Thermometer


OBD2 adapter with software for the laptop! $10.50
New ELM327 V1 5 OBDII OBD2 Can Bus USB Auto Diagnostic Interface Scanner | eBay

I am a little over $60

 

Considering Harbor Fright gives away their cheap multi meter with any purchase, I'd save the $5 and just get the freebie meter. They're all junk, but for free they'll get you by in a pinch. If I had a choice, I'd spend $1-$2 at HF for a 12 v. test lamp instead, as I've got them laying all around my cars, and use them often for quick testing.

If I was spending $100 on various "must have tools", my list would be short.
Multimeter-HF-Free
12v. test light.-#4288 $2.50 or the 30779 for $4 (better!)
Wheel/balancer puller-#69889-$13
Balancer removal/install tool-# 40749 $20
Grease gun-#66664 $17
circuit tester for amp load-#67725 $15
Compression tester-#69885 $22
Engine vacuum/pressure test gauge-Ebay $15

$106, but close.