Food = anything gross. Look online- there are tons of ideas for wonderful foods. http://www.toppartyideas.com/gory-foods/
I like the idea of making a "zombie corpse" with lunchmeats all laid out as the body on the table (uses a skeleton head, celery sticks as ribs etc..there's a pic of this somewhere online. The kids can make their own subs (word of warning, I learned the hard way: if kids are eating subs, they MUST SIT DOWN at a table, or you will end up with vinegar/oil all over your floor..and it's NOT easy to mop up.)..or make a "meathand" (Google it)and have them make their own hot meatloaf sandwiches. Try to get as many recipes for food you can make *ahead*...you do NOT want to be stuck in the kitchen with a pack of 11 years old in the house. Make sure to have lots of bowls of chips & munchies..I'm not big on putting out sweets for kids (other than the b day cake) as I don't need them hyper in my house. Are you making the cake? I've seen a simple but impressive graveyard cake made in a 13 x 9 x 2 cake pan & using store bought cookies as gravestones. Make a frozen head & hands to float in the punchbowl...hang shredded garbage bags or plastic tarp from doorways....
I always keep 2 games in my "back pocket" as there always seems to be time left over & nothing for the kids to do. I pre-blow up a bag of long, wiggly balloons & keep them in a garbage bag or two.When party gets slow, I throw them on the floor. The kids are then told they can play "swords" with them, etc. Once that gets to be no longer fun, I tell them they need to pop all the balloons by sitting on them (if you have pets, make sure none are in the room & make sure every piece of balloon gets picked up). The other game is....Butt Darts. Use a milk bottle or narrow vase...kids holds clothespin in their..uh..."cheeks" and has to walk over the bottle and drop it in to earn points. Trust me - no one will care about earning points....
You can print out paper coffin goodie bags, cool masks & favor toys here: http://ravensblight.com/papertoys.html
or take the web addresses to your local print shop & they can print them out.
I like the idea of having lots of games for kids, as NO ONE does games anymore at kid parties...and an 11 year old is at the tail end of parties...soon, they will be too "cool" to have b day parties. To get their goody bags, you can decorate a sheet or big piece of cardboard with a graveyard scene and put it in a doorway...make a stick with a piece of yarn & a clothespin on the end....each takes turns & they have to fish up a zombie coffin out of the graveyard...someone (dad? older sibling?) on the other side clips a goody bag or coffin to it...& kid pulls it up & over. Or you could keep the joke going by having the kids accidently pull up a bag of gummy worms..."dirt" (crushed Oreos) a stretchy skelly/some cheap toy..a Bluckie arm...til they finally get their goody bag.
I could go on & on...I LOVE planning kids parties.