Magnet - The Essential Basic Tools of Watchmaking
You never want to work on a watch without a magnet nearby! Not too near though, as you don't want to magnetise the movement.
I've lost count of the amount of times a part has either dropped to the floor or sprung across the room never to be found again. This is where the humble magnet comes to the rescue, except for brass parts!
You could spend hours feeling around the floor with a torch trying to find the tiniest part; with a magnet this task becomes so much easier. I've seen all sorts of homemade magnet contraptions, but from my experience you just need the widest and/or strongest magnet you can find to minimise the amount of searching effort required, ideally something that doesn't require you to get on your hands and knees every time.
There are various options available, from basic metal detectors to magnets on the end of a stick, or just a plain magnet.
When I initially searched, the longest magnet I could find was 10x1x0.5cm, which wasn't ideal but still useful for the low cost. It wasn't until later I discovered the Bergeon Magic Wiper (7871-1), which is basically a piece of card that you can fold to form an oval grip with a long magnet strip along the 28.5cm edge. This allows me to cover a lot more ground, a lot quicker.
Rough Cost: Basic Magnet = from £2
Bergeon Magic Wiper (7871-1) = around £14.50
Recommendation: Personally I would recommend purchasing the longest and/or widest magnet you can find even if you need to customise it a little for your needs. The more ground it covers, the quicker any stray parts will be found.
If you think I've missed anything or have anything to add, please comment below.