My experience with including 'RSVP by' dates on invitations has shown that no one actually pays attention to them. Seems like most people look at the party date, figure they'll RSVP at some point, forget about it, then remember a day or 2 before and RSVP. I've learned to send nudging e-mails on the RSVP date or the day after, and have found that people tend to respond to those e-mails right away.

Also, always have a few extra goodie bags.

speaking as someone on more of a budget than many of the other parents at my DC's school, I would certainly tell people if it's too late to add more people. (Sometimes it truly is! Some venues won't even allow people beyond a certain number.)

That said, if things were that tight, I'd probably send them a warning email around the time of the rsvp deadline. Just saying "I haven't received your rsvp, and just wanted to check with you before I give the venue my final numbers. We still hope Larla can come, but if she can I need to know by the day after tomorrow, as I will be giving them the final headcount then. "

You can just give my kid's favor bag to one of those who RSVP'd late.

I usually buy the stuff at Target with a few spares. I return what I don't give out after the party.

I get this all the time. Lots of parents don't RSVP and the kid shows up or others RSVP yes and don't bother showing up. I never know how many will show up. It is so frustrating - I just make a few extra goodie bag and try not to get upset. I just give the extra goodie bags to a siblings who tags along for pickup - they love it!

I had this happen once and I just told the mom that we would happy to have the kids, but I told her I had bought favors for the exact number and might be short so I might have to get her one later. She didn't care, she just wanted to come to the party and my DD was glad she came. Ended up having a no show, so we were okay with favors.

I had a similar situation arise, and said yes to the people coming. However, I just broke up a few bags of favors among those kids so that they got a little something - by the time the sixth parent did a later RSVP one day before the party, I was out of extra loot bags and felt no obligation to run out at the last second and buy more or different stuff. The kids still had a good time, and didn't even mention the goody bag difference.