I recently made a fire kit out of tea tin. It's bigger than an altoids tin, and doesn't have a latched lid, so there no holes to plug. As long as I don't overstuff it, the lid is a tight fit, but I secure it with elastic or tape anyway, just to be sure.

I like carrying a metal tin to use for making char cloth, but that requires a hole in the tin so it's not going to be waterproof anyway. In that case, I include the tin as part of the kit, and house it all in something waterproof, usually a zip lock.