The challenge for me--and for many road warriors, I'd bet--is that I hate to be on a trip and realize that I don't have the right cable for something I need to do. So as much as I want to leave certain cables at home, I'm paranoid that the one I leave behind will be precisely the one I desperately need just before my big presentation.
Fortunately, there's a good middle ground. Instead of carrying cables, I carry cables. A 6-foot FireWire cable? Try 6 inches. A tangled-up iPhone cable? I prefer a 3-inch connector. Swap out a couple bulky, lengthy cables for smaller versions (or just-as-capable adapters) and you'll cut down on a bit of weight and bulk. Swap out of your cables for travel-friendly versions, and you'll be amazed at how much lighter your laptop bag is--and how much neater it is, as well.
To give you an idea of what I'm talking about, here's a photo of the various cables and cable adapters I carry with me these days, along with a short description of how I use each one.
This may seem like quite a bit of gear, but the picture to the right shows how much space everything takes up in my bag, compared to just Apple's extension cable and the FireWire cable for my DV camera. I've got everything but the power cable in a 5- by 7-inch ; the clear side panel is useful at airport security checkpoints.
The biggest caveat to going small is that your range is limited. For example, my DV camera or iPod has to sit right next to my MacBook while connected. I rarely find this to be an issue, though; I've usually got my computer and all its accompanying gear on the same desk or table--often the desk or table--in my hotel room.