An underappreciated and underutilized force for wargaming (particularly as it can be made with existing surplus equipment), the UN standing army as discussed in books like A UN Legion. Unlike some other entries in Weird Wargaming, the nature of this force makes describing it in any exact detail much harder.
On one end, there’s light peacekeepers with nothing but small arms or vaguer proposals. On the other, there’s the incredibly detailed “Vital Force” proposal. The bigger “world army” proposals also tended to be the most vague in terms of equipment. Yet it’s easy to find analogous historical units. Either the entire force or a large chunk of it could easily be structured like existing high-deployability forces. Airborne and amphibious units provide an excellent, well-documented guide.
For “world armies” with more conventional units, there’s plenty of national and/or theoretical inspiration to be drawn, possibly with some inferences (for instance, a priority may be on allowing smaller units to operate as independently as possible). The heavy divisions in the rapid-response units may get prioritization for upgraded equipment. As for that equipment, it can be anything from purpose-built (especially if it’s intended to be airdroppable/amphibious) to surplus.
The proficiency levels of a “small force” should be high, as creating a handpicked, well-trained force over clunkier ad-hoc formations is the entire point of their existence. Bigger “world armies” are going to be inevitably diluted, but should still err on the side of greater skill.