Under 1 kilo without food and water can definitely be done, depending on your expectations for the pack.

The little pack I use for short day hikes/trail-running weighs 4lbs 11 ounces with water and snacks, without water it weighs under 2lbs. I started with a Camelbak Hydrobak, which holds 1.5L of water. Then I added the following:

-2 Cliff bars
-1 packet of peanut butter

-Princeton Tec headlamp (no strap, mounted on the pack's own strap)

On a mini quick-link attached to outside of pack:
-BSA Hotspark
-Fox 40 Micro whistle
-Leatherman Style PS [replaced the scissors for a knife blade]

Plastic ziploc bag with:
-Disposable poncho
-Coffee filters
-brightly colored bandana
-Spare headlamp batteries
-moleskin
-package of tissues
-MP-1 water purification tablets
-small plastic signal mirror

It's not exactly an over-night bag, but it's small and light enough that I don't even notice I'm wearing it. Therefore, I've got no excuse not to have these basic supplies with me, even if I'm just going for a short walk in familiar territory.