Being active mil I’ve rucked with just about everything you can imagine. From sandbags wrapped in 100mph tape, plates from the gym, to the equipment I’d actually be carrying in the field. Lately I’ve been a big fan of these cheap dry bags from Amazon filled with sand. Got the idea from MTNTOUGH. Really like how quick and easy it is to switch weight. You can also pull out weigh easily to use for other exercises. This is super nice if you are on the road traveling and don’t have access to a gym. I think I paid $35 for a 5-50lb weight range.