In cold weather, coat your feet with antiperspirant for several days before a backpacking trip. This will stop them from sweating too much. This means drier, and therefore warmer feet.
Don't use a pack cover. It is just too much extra weight. Most packs are relatively rainproof now in any case. It can help to put the contents of your pack into several plastic bags, just in case the pack leaks. This will add about an ounce - much less than any pack cover.
A whistle can be a good thing to have in an emergency. If you bring one, make it a simple plastic one. If it weighs an ounce, you bought a heavy one.
Bring a radio if you really think it will add to your trip, look for one of those little ones that attach to your belt and have a tiny ear plug. They weigh less than two ounces.
Hiking Gear To Avoid
If you really want to go light, avoid anything that is just "gimmicky," and doesn't add any substantial convenience or value. In this category I would include seats, reflector ovens, forks, coffee pots, neck coolers, binoculars, chemical hand warmers, electric socks, thermos bottles, cups, thermometers, towels, shaving mirrors, tents, and sleeping bags.
1. Be sure it is useful, and not just interesting, before adding it to your packing list.
2. Keep your hiking gear lightweight.