For gear, start with the Scout Outdoor Essentials listed on page 224 of the Boy Scout Handbook:
<>Pocketknife
<>First aid kit
<>Extra clothing
<>Rain gear
<>Water bottle, filled!!
<>Flashlight
<>Trail food
<>Matches & Fire starters
<>Sun protection
<>Map & Compass

In addition I'd include:
<>Whistle on a lanyard
<>Insect repellant
<>1/2 roll of Toilet Paper in bag
<>Something bright orange for signaling - this can be an orange trash bag, an large orange bandanna, etc... A lost Scout huddling under his dark green poncho can be VERY hard to find without some kind of bright flag displayed.

The pocketknife can be stowed in their bag and left there if they don't have their Whittling Chip card. I personally like boys to have two knives - one Swiss Army Knife with scissors and a locking blade knife. Personal first aid kit contents are described on page 289 of the Boy Scout Handbook. For Webelos you wait on the mouth barrier and eye protection. As mentioned by someone else, extra clothing should include a synthetic jacket and hat - enough to get someone through the night if needed. For a young Scout a nylon (not plastic) poncho such as those available from Campmor.com is fine. The water bottle(s) should provide at least one quart of water and be filled BEFORE leaving home. The flashlight (AA-sized) should have new batteries or extra new batteries should be carried too. Trail food is important on a hike - bring enough for a snack plus extra if needed. Matches and fire starters should be stored in a waterproof container (doubled ziploc bags). Sun protection should include a brimmed hat, sunscreen, and lip balm. A very simple baseplate compass is sufficient for Scouting, though in many parts of the country adjustable declination is very useful. Leaders should provide each Scout with a map of the area before heading out, unless other arrangements are made ahead of time. Even simple park maps are better than nothing. Make sure the whistle is on some kind of lanyard. Check with your local highway department for orange plastic bags - they are great!

As others have said, the most critical thing to teach them is to be ready to accept that they are lost and to stop, put out the signal flag, and stay put - help will be on the way soon.

The Scouts need to be told to have fun, keep their essential gear at hand at all times, to use the buddy system, and to let leaders know where they are at all times. Leaders need teach the Scouts, enforce expectations (the essential gear does no good sitting inside the tent), and take headcounts on a regular basis.

Ken K.
(4 years Cubmaster, 5 years Den Leader, and now an Asst. Scoutmaster)