We had great success at that age with various "treasure hunts" in the backyard. For a safari party I got a bunch of little animal themed toys at
http://www.orientaltrading.com/ and hid them around the yard. We got some of the "color your own" gift bags and had the kids color them in, then we set them loose in the yard to find the animals, which they then put in their bags. And that takes care of the "goody bag" too!
We did the same thing a year later with an alien-themed party, using alien stickers and markers to have them decorate plain gift bags before looking for little alien toys in the yard. The kids loved it, even though many of them had already done it the year before.
A couple of years before that we had a "fishing" game, where an adult hid behind a big table on its side, decorated to look like a pond. The kids had fishing poles made from wooden dowels, string, and a clip on the end. After they tossed their "hook" over the table, the adult would put a little toy on the end.
For the cake, my kids often liked rather obscure characters which were hard to find decorations for, so I used to print out characters on the computer, cover them in contact paper, and staple them to small craft sticks. Then I would stick the sticks into the cake. You can make a cake for almost any theme that way. (And my kids would often play with them as puppets after the party was over.) I've attached a picture with a Mario Kart cake that we made a few years ago...I had the bakery make a "race track" and I added the characters.
Hope those ideas help...we've done lots of different birthday parties here!