I wouldn't get too hung up on party games at this age. When my DS was 3-5 years old all they wanted to do was run about and play on equipment. Even at home, with just ride on's in the garden and a few boxes of DS's toys, you'd never get them together again once they started! Trying to get them all together, having just got onto a slide or the bouncy castle, can be a nightmare as they don't want to leave it! So you either start with that - before they even look at the play area - or leave it.
Be careful with the bubble machine - make sure the bubbles stay off the bouncy castle as it'll make the surface slippery. Lesson learned there ages ago...
Drinks wise for the parents, I'd offer a drink ('what can I get you') when they arrive. To save you leaving guests if they're late, see if you can rope in another parent or your DP to get the drinks as people arrive or you'll be trying to keep an eye for new arrivals, ordering drinks and supervising! Or wait until they're all arrived, settled and chatting then get an order of drinks. After that it's fairly easy to offer another if you see empty glasses or just tell people they can buy their own. If you want to offer to pay for drinks just explain it's tea/coffee or soft drinks and make sure the bar know that. They'll be used to that sort of thing so they'll guide parents. At soft play areas for birthdays we just used to get a tea/coffee/soft drink then offer a top up as we saw people needed them. Often people would beat us to it and go off to buy a couple of coffees. Parents are usually chatting with half an eye on the little ones so they're not going to be too fussed (we were always grateful for a sit down with a cola!)
One thing I will say is to say to parents the kids get their food first. We had that as a rule after one mum filled her plate leaving not a lot of choice for the kids. At the end of the day it's a party for the kids. Normally parents will get their little ones a plate of what they like, get them settled then 'nibble round the edges' as far as feeding themselves are concerned. I got really used to grabbing a handful of crisps then dashing off to supervise DS or join another mum to break up a fight over a swing! But if you just say 'the food's ready, can we get the children sorted out first then help yourselves' they'll understand and it stops the parents filling their boots whilst a three year old watches the sandwiches disappearing!
Yes to the goody bags. And yes to putting names on. Even if they're the same. As one PP said it helps to know who has had a bag (you may find a number of little hands ready to grab), and it helps if a bag has been left somewhere, no-one else's bag gets 'found' by mistake only to find the person's whose was missing now has two... (again, lesson learned...) Give them out with a 'hope you had a really good time' to signal the end.
One last tip, if you're giving out cake at the end (we would put a piece in the goody bag to save the kids trying to juggle) wrap the cake in foil then in a napkin. If it goes into just a napkin it'll be a squished mess as the icing will seep.
Have fun!