Field Notes and Field Numbers
Field notes and field numbers are great ways to record details of collecting events and ultimately form the basis of locality labels. But they're also a good way to keep a record of your trips and can be used as a shorthand in the field, which lets you focus on collecting and not on writing localities on small containers.
It really doesn't matter exactly what you use but I have a Rite in the Rain notebook cover with a size B6 notebook inside. This slips easily into a side or back pocket and lets me keep a running log of when, where, and how I'm collecting. Cheapo mechanical pencil, fine tip marker, notebook. That's it.
I mean, there's not a lot too it beyond writing down what each number means in the book and writing the number on the container the bugs are in. I get GPS data in the field and keep track of specimen associations such as plant identifications, water bodies, weather, types of collecting equipment I use, and general behavior. You can include as much detail as you want, but it makes your life easier no matter what. This is usually what people collecting for scientific purposes are doing, albeit with a wide variety of goals and documentation. Some researchers focus on phenology and so note a lot of habitat and behavioral information. For example, collecting pollinators can involve a lot of this as the climate, weather, and plant community all contribute to which insects are active and when. Detailed records can be very valuable, especially with repeated visits to the same places. Whether this is your local park or favorite camping spot the key to the strength of this kind of data is consistency.
Maybe not all of that makes it onto the locality labels. But a lot of it can. And the truth is you don't need pages of notes to make good labels. Even just GPS coordinates would help you keep track of collecting events. But when someone is trying to retrace an old collector in the future it's nice to have a plant name or trap type at the very least. To be honest it's unlikely full field notes would be known and accessible after the collection has changed hands so the label will likely be the last say.