Birthday parties are the best thing in the world... I enjoy them more now, than when I was a kid... (I'm not or ever was a JW)
Believe me, there will be sugar, sugar, and more sugar... so don't bring anything that contains sugar, especially if it is for the parents... but usually people don't bring food to a birthday party unless it is a family party... then sometimes... but bringing it is ok... my advice, bring either a veggie platter with some sort of dip... I usually have carrots, celery, peppers, colliflower or brocholi.... and put in a lowfat ranch dressing in a bowl in the center... or a veggie dip found on the back of a lipton veggie soup box... or bring a fruit salad... most parents want to stay away from the stuff for the kids if they are trying to eat healthy... so they will be greatful to see veggies or fruit...
and for the gift... usually I don't spend over $20... something the kid will enjoy... even if you ask the parent that is fine, or ask another parent with a child the same gender and age what their kids like.... toys, games, puzzles are always good...
and most of all... Don't worry... you and your kid will HAVE FUN and can't wait to go to the next one!!!!