I think you made a good choice practising with the inflator. I once was quite a way from home and only got a partial inflate with one co2 capsule so went for another. The sound of the inner tube exploding sounded like a gunshot and had some poor chap out of his house asking if I was ok. 
Fortunately I always carry two tubes, so all was well. I could have exploded the tyre, again lucky.
It’s a chain gauge. Chains are consumables, like brake pads and cassettes. How long a chain lasts depends on how many miles you do and how you ride up hills. Shifting late whilst grinding up a hill out of the saddle puts a lot of stress on the chain.
You can get a core extractor for the price of a beer, which can help, a spoke key will also do the same job.
What you really need is a handy toolkit all in one, like this one that @Derbysieger made me so envious of. I ended up ordering the same kit and it’s great for your home bike repairs.
These tools are like extra planes for your favourite sim. They sit there until you need them, which isn’t very often, but when you do it makes the job more pleasurable. 