What's the easiest way to prototype a board game design?
Your instinct is correct. In the first stage you're only interested in seeing if your mechanics are feasible so all you need are some abstract representations of your game components. A game may consist of roads, towns and cities but to test, all you really need are three different things.

You can either:


Repurpose components from other games
Have a collection of generic components in various shapes and colors (Maybe even something like Piecepack)
Do everything on slips of paper or cardboard


Anything beyond that would probably be overkill at this time. I've recently read an article about 3 German game designers (1 aspiring, 1 first-timer and 1 "pro"). Among other things the article described the pro's design room, which had a huge selection of meeples, dice, cubes, chits and other generic game pieces in various colors. Such a selection takes time and money to build but is probably the fastest way to test an idea.