A two year old is not going to remember her b-day party, so try to keep it as simple as possible, or you will have a melt-down on your hands. Make sure you (or someone she loves) can give her full attention that day, and don't count on her entertaining herself. It is pretty weird for a little person to be the center of attention from all of these people that are not usually doting over her, and then to boot, mom can't give her attention because she is too busy greeting everyone and setting up the food! She may not be thrilled with this situation and have a meltdown. Keep the "social obligations" to a minimum for her (Don't require her to greet each guest, for example) and DO NOT open the presents at the party. That is too much to handle and then you or someone else may expect repeated "thank you's" when she just wants to play with gift #1 and not move on to the other 12 gifts!
OK, so to answer your question - a baby pool loaded with turkey basters, toy fish and nets to catch them, cups and pouring implements of various sizes - you get the idea. If there are enough cool things, the kids don't need to get into the pool if they don't want to, they can just reach over the side. Or, do the same thing with sand or beans (in large sterilite containers, for example). Another hit is bubbles with various bubble wands and flyswatters for all to make bubbles. Also bring all of her musical instruments on a blanket and have a little CD player playing kids songs. Keep the party to 2-3 hours (which is a long time for little people) and do the cake in the middle of the party. I don't think organized games will fly because 2 years old is such a diverse age, so some kids may understand that there are supposed to be rules and other kids won't get it, they just wanna play on the swings, way too much frustration and organization for a 2 year old!
I think parents can get so excited about having b-day parties that they don't realize how much it can overwhelm the kids. For my 3 year old, we did the same thing, party in the park, bubbles, playground, picnic food and cupcakes with 4 friends. She is still talking about how she loved that birthday party because her cupcake had BLUE frosting and everyone else's was white. Ahhh youth!! Enjoy simple parties as long as you can, because when they get to be 9, you will be required to take 10 friends to Disneyland for the party!! Have a great time!