The Avalon Hill Gaming Company's board game Outdoor Survival (OS) gets a great deal of mention in the OD&D boxed set booklets. More than one person has questioned why, since everything needed to run a wilderness campaign is already in the rule books. The answer is rather simple: you need OS for the map board.
If the party became lost while in the wilderness, the map/board from OS came into play. This is why there are no rules in the OD&D booklets for generating random terrain: there was no need. When the party found its way again, they were moved back to the larger terrain map (Ah, yes! We're 6 miles south of where we ought to be!) and play continued from there. If players moved off the edge of the map while lost, Gary would just have them reenter from the opposite side.
The map really is handy, but with a sheet of hex paper, some map colors, and modicum of imagination you can produce something just as good. There are also a variety of maps for free created for D&D types of games available on the internet.
On a side note, I'd suggest using 6 mile hexagons for your outdoor maps as opposed to the 5 mile hex recommended in the rules. Why? Because character movement rates are generally divisible by 6 not 5. This small change will greatly ease referee burden during overland travel.