Last I checked, ammunition cans came in various sizes reflective of various calibers. many surplus stores in most areas carry several good condition cans for aprox. $5 to $20 depending on how much of a whore they are.
Draw up and cut a stencil, paint over the original copy with your own ammunition specification, and fill with bags of the appropriate ammunition - different BB weights(i.e. calibers) in different sized cans, obviously with a brand that will appease the masses. Scrap metal plates on the bottom inside adds to the weight and realizm, if required.
Canadian tire sells various plastic bins in different colors for usually less that $5 CAD each.
Place ammunition cans into plastic bin. Source scrap wood palettes (game hosts who build props are usually very resourceful and are able to find many of the items they need for free/low cost). Build carry handles out of nylon strap and attach securely to sides of palettes. Strap or bolt (your choice) plastic bin onto palette - you now have what would be considered a resupply drop skid similar to what would be dropped via airlift.
Said resupply skid can then be manoeuvred either by hand or by vehicle throughout your AO, with or without security elements. Talk about a HVT.
This was done before more times than one successfully in hosted Airsoft MilSim games, as thus is not considered a 'wild conceptual idea', but rather an attractive Game Element feature, particularly for those who are looking for as many real world MilSim elements that are generic in nature and compatible and feasible in Airsoft games. There's quite a list of those.