God, I'm about to be struck off MN - I love doing party bags.
To be fair, DS1 is 4 and thus far, his parties have been staid events with 4 or 5 of his friends that he's known forever (antenatal group!) and I know the mums very well, so no angsting about whether my card's going to be marked for putting in too many sweets/too much plastic.
Last time, I got some cheapy white paper bags off ebay, set DS1 to decorating them with stickers and foam shapes, etc, and inside put a mini sticker activity book from Amazon (cheapy cheap), a 'rainbow' pencil from a £ shop multipack, a small tub of playdough I'd made with nice smells (orange, mint, lavender etc) and a little galvanised metal bucket (ebay again, v cheap in multipack) with some cress seeds inside to plant. And some haribo packets.
And yes, tbh, it was as much for the mums as for the DC - I know them as good friends and knew they'd enjoy faffing about with the seeds and cute buckets.
From now on, it'll be parties with his school mates too, and probably more guests, and I'll be going down the time-honoured route of: slice of cake, some sweets, balloon, pencil, bouncy ball. I wouldn't ever want not to do them though - I really enjoyed getting them as a child and DS likes giving them (and getting them).