Now materials have their own caps you just start to "ignore" them as they fill up. There's no need to drop mats
This.
I'm guessing that the scenario, here, is that the OP's blowing up Sentinels, dashing over to the debris and is finding that it's all stuff that he's already maxxed-out.
In that case, stick it on your Ignore list (from the Left HUD Contacts tab) and you won't see it on your scanner any more.
If you do that, however, you need to remember that you've done it so you can take the thing
off your Ignore list again when required.
That can be a nuisance too.
If, say, you've maxxed-out your stock of Arsenic and you're somewhere that has heaps of Arsenic (!) you might decide to put it on your Ignore list.
You then do a heap of upgrades and use up a heap of Arsenic.
You then, possibly weeks or months later, notice that your stock of Arsenic is running low.
You go to look for Arsenic but, despite shooting the appropriate things, none shows up.
That's cos it's still on your Ignore list.
You need to shoot stuff, look at your Contacts list, see if there's any Arsenic there, highlight it and then remove it from your Ignore list.
All a bit fiddly.
Might be better if there was some kind of option to manage your Ignore list manually.
We already have a list of all known mat's in the right HUD.
Perhaps an option could be added to
that which allows us to ignore/un-ignore each mat'?
As for Guardian stuff, specifically, I don't think you can trade any of that, anyway, so it's just a case of grabbing what you can, managing it via the Ignore list, and then going back for more if required.
Trading won't help with Guardian mat's.