For a game of OGAM, you’ll need at least 6 six-sided dice. It is better if three dice are of a different color. You’ll need the rulebook (of course!) and three measuring sticks (you can build your own or purchase the official ones pictured below).
You will need figures, of course. The default scale for tournaments is heroic 28mm, just like the official OGAM figures produced by Northstar.
However, nothing stops you from playing in other scales. Just check with the local players. The rules are not scale-dependant in any way, and the required play area is quite small. The small size of an army (15-20 figures if playing at the default value of 900 points) makes the game very affordable.
If you use open order troops, like units of skirmishers, you’ll need a flocked, spent compact disc or a circular cardboard base of the same diameter per every unit. CDs are used as movement trays for open order units. Generally, one or two CDs per player are enough.