Pressure cookers don't weigh too much, mesh. Maybe 10 lbs for smaller ones, and given that this shithole was planting them and moving they couldn't be that big. A box of nails weighs may e half a pound for several hundred, and ball bearings depend on how big and what metal. Add your explosive cocktail recipe and the overall unit weighs under 25lbs I'd say. Easy to carry 1 or 2 without much effort in a sack or backpack as they did. It'd make for a very easy placement and evasion, allowing for one guy to do the work and seem less conspicuous. Honestly I'd be surprised if anyone else was involved in this, as it seems designed to be quick in and out.