I've been running for a while now and regularly do half marathons...got one this weekend, in fact. I would never be able to go running without my meter and some sugar, I personally can easily mistake the feeling of being knackered from exercise with a hypo.
I use two different things to carry my stuff around with me. The first is a bumbag, not the height of fashion, but does the job. The second, which is use on longer runs and trail runs, is a Camelbak. These are water backpacks with pockets in.
I always take my BG meter and a load of dextrose. For the distance of a half marathon, I'd say it's a must to take these with you. For road running, I'll probably have 4 packs of dextrose for a half marathon, it it's a trail, I'll take more.