SO, I've been progressing! Here goes!
I found really beautiful cotton tablecloths on clearance at a local store and I found a few extra at goodwill. They will be perfect! I also found cloth napkins there too- 8 for $3!
I also picked up at goodwill 40 regular metal forks

. I ordered some plates and cups. They are plastic, but dishwasher OK. I really thought about the ceramic, but the kids are so little and so much could shatter... Plus, they are a LOT heavier to tote to the park. The plastic are washable, reusable and recyclable, so I left it at that for now... It's better than use once and toss, right? A work in progress, I guess...
I decided on "ice cream cone cupcakes" (like these
http://home-and-garden.webshots.com/...57033965iKrtsW... they are cupcakes baked in an ice cream cone! No paper wrappers, no box... maybe even no plates?). I bought a special carry case for them (a bit of a splurge, but I'm hoping to make them again, as I can get nice cake and frosting mixes from Whole Foods). My son picked out sprinkles and he is really excited.
I decided I will use our red wagon to haul everything there with 2 (clean!) containers that came with the kitty litter (they are big and yellow with lids) for compost and dirty dishes/silverware to take back to the house.
I made up evites.
And, I made decorations! This is the best part, if I do say so myself

. I found these beautiful coordinating pre-cut strips of gorgeous jeweltone batik fabric (kind of like this, but not quite- more vibrant pinks and reds in there
http://www.twinorchardstextiles.com/...k-Jelly/Detail). I got clothesline and fabric glue and cut them in half then folded them over the rope and glued them on (think: like a banner). I made about 100 ft (in a few sections) and it took me about 3 hours. I am about the least crafty person alive. This was really, really easy. I had them up to dry in the livingroom overnight and my son woke up and they literally took his breath away

. He gasped and asked if they were really for his party. Aww! They are positively delicious when the sun shines through them and flutter in the breeze. They will be amazing at the park! Really, these might be my crowning crunchy party glory!
I'm also saving a few babyfood jars to decorate the tables with whatever "weed flowers" I might pull from our yard (dandelions, bindweed, an overgrowth of sunflowers or pansies).
I love the idea of a jade plant. I don't have one, but maybe I will get one

. Fairy houses are super too! I have some odds and ends from other craft parties, so maybe I will pull some of those things and have a hodge podge.
A friend recently did a "nature treasure hunt" (looking for clovers and ants and dandelions and the likes) and I think I will steal her idea

. I'll bring some chalk and bubbles and maybe some sand toys as well.
I was also thinking of buying an ice-cream maker.... Just 'cause that's fun.
This is taking a lot of intial investment (maybe, $200?)... but I keep thinking that the next parties for both kids over the next 5-10 years will take so little! No decorations or plates to buy, no cake to order... basically a few inexpensive food staples and we're set! I'm sure they will have "requests" as they get older, but we'll work with that.