First of all, Agents are very good in dodging bullets (or finding human shields). So, even if you had all the fire power displayed in "The Construct" (infinite white room), you can only use a maximum of two fire arms at any given time. Miniguns are really not portable by human beings (we see one attached to a helicopter but you couldn't both carry it and aim). So you would have to use military style rapid fire weapons. Something that really doesn't impress Agents.
Now, when it comes to actual tanks and tank-like vehicles. What would you accomplish? Humans usually infiltrate large cities. The regular military would be enough to stop a bunch of tanks rolling into a densely populated area. Hence, not an option either.
Automatic drones are typically intelligent (whether they operate in a computer environment or in the "real world") and the humans don't really have the expertise to create artificial intelligence (anymore). They are refugees and underground fighters, not scientists. Furthermore, humanity made bad experiences with artificial intelligence, so the (very spiritual) council would not readily grant research into such advanced warfare drones even if they had the know how (even remotely), which they certainly don't. Note that all their technology comes from a pre-war era and they barely manage to keep it functioning.
In addition to it being really really hard to bring down an Agent (see above), it's utterly futile. Even if you actually succeed in killing an Agent, you merely killed its human host (something that the free humans would not be particularly inclined to do if not really necessary). They can instantaneously repossess any nearby civilian. Towns tend to full of those. You basically would have to wipe out an entire city. Not a very covert operation.
That's an in-universe answer, but the more interesting aspect are the metaphorical and allegorical implications. Humans are supposed to be held in bondage by technology, either physically (like the people living inside the Matrix) or psychologically (like the people living in Zion). This is an allusion to our own dependency on advanced technology for our survival and every-day life. It wouldn't make sense for the humans to use technology for their fight against their dependency on technology.