Well not necessarily prepping or survival but somewhat related... I've been using Fiebings mink oil. Remove laces and just rub it in. Extra on stitches and edges. Sit overnight and brush with horsehair brush on am. Seems to work ok but leather seems a bit "greasy" and not sure its 100% waterproof (boots seem damp on really wet days but could just be cold). Probably do this once a month but don't really keep track. One things for sure leather is very soft and well formed after a few months. So what do you guys do?