Did you know that modern ammo pouches, purses, and messenger bags can make fantastic belt pouches and satchels for carrying your gear? Now you do!
All you have to do is avoid obvious logos or printed patterns as they tend to clash with the aesthetic of certain periods. Thrift shops, stores like Walmart, and even some hobby stores might have what you need when it comes to a cheap purse or other bag.
When it comes to belt pouches though, you have a slightly wider variety of options. You can easily make your own with a bit of sewing ability and leather, you could add belt loops to a smaller purse, or you could make use of old ammunition bags! Depending on the weapon and capacity the pouch is designed for, they can prove quite handy for storing potion vials, money, or small kit items.
You can also find chests to store your extra gear at Hobby Lobby and similar shops. Just get creative!