Sunnydays,
Falken is probably right about the best bang for buck. I may have been the one that mentioned SPS initially. Ordered a bunch of bulk reagents a couple years ago and they were shipped in a couple days directly from Taylor. Even with 2 oz bottles you will find the CYA reagent will go first, followed by the Calcium Hardness first reagent. Think R-0010? The 20 drop one. Not near the kit now. I keep the big bottles in the fridge and only open them when I refill the smaller bottles. Stuff will last for years under these conditions.

Iwannapool,
Free and combined chlorine
pH
Total alkalinity
Calcium Hardness
Cyanuric Acid

The base and acid demand tests are almost useless.
If you have a salt pool then a salt test too.

Al