Undead Labs are aiming to give players a feeling of genuinely surviving in a world ruled by shambling corpses. To make that work correctly, players are going to need lots of little touches here and there to reinforce just what has gone wrong and what sort of threat living humans are facing. In the most recent set of questions and answers from the development team, more elements of the environment and interaction with same are spelled out, giving prospective survivors an idea of what to expect.
While the game isn't planned to be an ornate physics simulator, there will be a practical limit to how much an individual can carry -- and while vehicles can carry more, the problems of noise and fuel will place some limits on stacking an SUV to the brim with heavy weapons. Hunting wildlife and handling aquatic environments will both be issues in the game, with the obvious caveat that humans drown far more easily than zombies. There are a lot of other interesting tidbits in the full rundown as well as some valuable takeaways that aspiring survivors would do well to internalize.