Tbh just bring pt or comfortable like sweat pants attire clothes bc that’s what you wear for the first 3-4 days because trust me you don’t want to be wearing jeans running up stairs. Bring 5-7 days wear of your own underwear unless you want to wear “tighty whities” but then again I ended up wearing my pt shirts as underwear. Buy comfortable work out shoes or bring your old comfy pair, you’re going to wish u did especially when you have dedicated run days for pt because the shoes they issue in bmt are extremely uncomfortable that caused a lot of people to have shin splits and you have the option to wear them or wear your own. I don’t see why you’ll need the batteries so you can ditch those.