I started out gluing a small, wooden dowel to each figure's base. I bought colored, plastic tubules, which slip over them with minimal resistance (hopefully, or they fall off when I tilt the figure!). I thought I would change the figures' tubules to create different Units, keeping the figures versatile, never locked into a particular Unit group.
However… I have around 20 different (fantasy) armies, and each army is broken down into different Units (Archers, Slingers, Spearmen, Light Infantry, Med./Heavy Infantry, and Cavalry). I need to keep Unit sizes between 8-20 figures, typically, for rules-based purposes to make game play less of an all-or-nothing affair (Units make Morale Checks for the entire Unit, so larger Units which fail, can really impede game play for the owning player if his armies consist of only a few, very large Units, and they Route…).
For my Army Men games, the Units are not all the same type of Infantry figures: some Units are solely Combat Engineers, but most Units are comprised of diverse figure types, including various Machine Gun types (Light/Medium/Heavy), and some Units have Forward Observers/Recon figures attached to them. At the table, I need to know which figures belong to which Units, so players do not lose track of their Units' figures as they move across the table, likely intermixing with their team members' figures. The figures used are the same castings, and they are on the same team/side, but everyone needs to know which figures belong to them, and which do not.
As I stated, I started out using wooden dowels attached to the figure bases (note the two colors of tubules on the dowel of the far right Stone Giant -- the underlying White tubule indicates he is a Unit Leader figure; all tubules are located in the same rear corner, for instant recognition of the figure's facing), allowing me to re-assign figures from one Unit, to another. This proved to be far too tedious, and excessive overkill, in real life.
I now glue the Unit marking tubules directly to the figure bases, permanently assigning the figures to pre-made Units. The 2nd and 3rd Stone Giants, from the right, in the photo linked to, above, have had their purple tubules glued directly to their bases, without any dowel, so these two are permanently attached to the Purple Stone Giant Unit. [Sigh of relief -- I never have to figure out their Unit, its size, composition, etc., again…]
I realized that I was very unlikely to truly need that level of organizational variability at the tabletop! It makes it sooo much easier to create static Units of figures: in this way, I can build armies using whole Units, without having to rebuild each Unit, for every single game I put together… It vastly streamlines Army composition, making game setup easier, more efficient, and faster. YMMV. Cheers!