No need to get so messy if you don't want to! Go to this link:
http://www.celebrateexpress.com/celebration/pages/product...
http://www.celebrateexpress.com/celebration/pages/product...
That first link is the Bob the Builder Construction Theme from Celebrate Express. The second is the First Birthday Party Consturction Pals Set. OR just go to celebrate express.com and look around and find a truck theme of your own. You can order SO MUCH from this site. I have used it for all my kid's and god son's birthday parties since I found it. Even my mom's!
At age one, you don't want too much going on for too long at the party any way, because one year olds *will* get over stimulated with a lot of people around. Really, you just want something for them all to have to open while he opens his presents if you're going to have others his age, something to do for a little bit while you have a few minutes of socialization and hand out cake, and then the cake and something to take home. Really, little kids parties shouldn't last for more than an hour or two at the most in my experience.
So, this site has a lot of things to keep the kids entertained. There are GREAT favors. They have Dump truck mylar balloons, candy tool sets, a party favor pack that has a little dump truck in it, stickers, play dough and play dough cutters (these all come separate so you put the box together yourself, which means kids too young can have play dough left out and you can add your own little things to go in). It has all kinds of decorations and fun things, too. You can get all the kids their own construction hats from here, they even have these adorable cups with straws that look like construction cones! They have construction traffic signs, toy flashing safety lights, a construction candle holder set for the cake, you can get construction t-shirts for the kids, a bulldozer pinata, etc.
Any set you get from there gives you the option of a thick vinyl personalized banner (They look GREAT), and come with a themed plastic table cloth, themed party ware, themed invitations and thank-you cards, and great keep sakes (like personalized framed mats and memory scrolls) for you.
I love planning parties and activities and I use this site all the time for it. My last one was my oldest son's third birthday party, which was a pool party Diego themed. We had an "animal rescue" adventure, which was just a scavenger hunt for little bean bag animals, swim time with themed pool toys, pull string pinata, favor boxes, and cake. He was worn out pretty fast, but a lot of the kids there were older, so that's why I had so many activities. My youngest son's first party was Land Before Time themed and since he was just turning one, I them all open their favor boxes while he opened presents (their favor boxes were actually buckets which had dino stickers, a couple of large plastic dinos, some smaller dinos, a dino-cup with straw, etc.), then we did his own personal cake and then everyone else got cake from the bigger one. After that, we were done. We did have some swimming with a kiddie pool and a bigger pool, but the party didn't last long enough for anyone to do much swimming.
Anywho, the point of that was... you want to give the other kids something that will make them happy and enjoy it, but don't do too much because the focus is on your one year old and he wont last long. I would try not to invite too many people over unless he is used to it, as well. My first son's first birthday party my uncle invited a TON of people that I didn't and it was just way too over stimulating. He was fussy and just wanted to nap.
I hope this helps and enjoy your sons party!