Hi, and welcome to the site.

I like using liquid test kits when I need an accurate reading. I do use dip and read strips but they aren't that accurate and will only tell you when there is a problem happening.
Good things to have handy are:
An unused bucket (never been exposed to cleaning chemicals)
An empty ice chest/beer cooler (emergency fish container)
A fish net (obvious)
A battery powered air pump (power outages)
A gravel vac or python-style water change system (for water changes and cleaning)
A magnetic algae scrubber (fun to play with, too)
Spare parts (airstones, filter pads, airline tubing, fish bags, etc.)
Activated carbon (adsorbes may toxins fast)
Zeolite (absorbs ammonia fast)
Rock salt