No-one needs to take two laptops on holiday, a selection of PDAs isn't essential travelware and there's really no need to carry a PMP, games console and dedicated ebook reader as well.
If you're really planning on travelling light then your gear should fit into a pocket or a couple of pockets worst case.
Which devices you deem necessary really comes from the type of excursion you're planning. For example if you're planning a safari then a smartphone's camera probably isn't going to be up to the job. The smartphone is essential though, so why not pick one with a decent screen and add a large memory card, eliminating the need for a PMP, ebook reader and games console in one swoop.
My current travelling light pack consists of an HTC TyTn, Nokia N800, Freeloader Solar charger and a couple of USB leads. I may add a bluetooth keyboard in the future. Ideally I'd swap the Tytn for a Nokia N95, adding GPS and a camera to my kit list without actually making it any larger or more weighty.
Its a fine balance between too much and too little. When you're days away from home is not the best time to find out that you have ditched a piece of kit vital to operations, so have a care when packing that you have the appropriate kit for your journey and nothing more.