pencil case - cheap, discrete & convenient
I use a pencil case, and unless I know I'll be staying out past evening dose time, I just take a pen containing my short acting insulin, plus a spare short acting cartridge and a long acting cartridge, which I can administer with either my short acting pen or the spare syringe that I also carry as back up. Plenty of space for name & address label, spare needles, a couple of plasters (for the very few occasions an injection bleeds and I'm wearing pale coloured clothing or for general scratches from other incidents), painkillers, tampons etc. All in a pencil case measuring 12cm x 20cm and about 5cm deep when filled, that cost about 60p from a supermarket reduced shelf. For slightly smaller capacity but more rigidity / protection, there are pencil / geometry instrument cases made of plastic or metal - remove the inner holders unless your pens are shaped like set squares, compasses, protractors or rulers!