I haven't played much of Only War, though I do recognise the method by which guardsmen are sent into the fray, with it being more about missions granted from a superior rather than tales of high adventure. From observation, it runs in a fairly different way to things like Dark Heresy or Rogue Trader where investigation permits a level of freedom for the former, and generally being masters of your own destiny applies to the latter. With Only War, well, things seem a little different, with party members following along with the rest of the army and having a lot of what they do being laid out for them.
Granted, I do know that being a scouting party might be a bit more free in how it works, allowing the players to explore an area then report back, with some hijinks occurring during this. I also know that it likely has more freedom than my initial observations give it credit for, but I had something a little different in mind.
I was hoping to run a game where the player's squad (either just the PCs or the PCs and about ten generic guardsmen) are separated from the rest of the regiment on a Death World or Feral World, with long range communication being prevented by an event immediately beyond their control (The current working idea is to have a global dust storm kick up due to some Chaos or Necron shenanigans, and the dust itself screws with the signal.)
This presents problems, obviously, with the group no longer given the luxury of resupply and reinforcement should things immediately go south, and it's difficult to run a game where, generally, the quality of your loot decreases and still maintain interest.
What I was hoping to discuss was how the resupply and reinforcement conundrum could be resolved, as well as some ideas for encounters that the group could have while searching for a way to regroup with the regiment. At the moment, I have volunteers from other standard imperial forces, impromptu recruitment from the settlements they might come across and even forces that come along from other systems (I doubt a tired group of guardsmen would turn down a Space Marine). At a push, and if they can be as diplomatic as they can, I might be persuaded to allow some Xenos back up, especially if the situation is dire enough to warrant an alliance, though I can't help but think that perhaps any other wandering imperial forces that spot a squad of guardsmen marching alongside an Eldar or Tau group would end in a far less favourable fashion.
As far as gear goes, the group will be stranded with the majority of their starting gear (so, if they're an armour regiment, they get to keep their Leman Russ, but they won't get a new one if it explodes, so it might invoke them to become a little more protective of their tank) but getting more comes down to looting and trading.