If you're just wearing it for 30 min, I'd go Alice Pack, but try to swing by a military surplus store and try one out before pulling the trigger to see how it fits. The folks that run those are usually chill and probably won't care if you load it up before trying it on, but I'd ask first lol. If you can find one, the older army packs, with metal frames, are the way to go. They can be better adjusted to fit your body and are bomb proof, but I've seen the newer plastic frame ones be put through tons of abuse