AGH! My sims forgot to make food or hire a caterer! What shall I do?

There is a buffe table in one of the earliest stuff packs (Glamour Stuff I think), there is also one in High School Years. 
You can also click on the fridge and hire a caterer. 

High School Years also has both a drink and a food table that works like a buffet table, just click on it and buy the food directly.

DJConnemaraDSMYou could also open the Gallery and search for "food" in Rooms!

Pause your game and go into build/buy. Get one of the banquet tables, place it where you want and then have your Sim click on it to serve food. I often do this, even when a caterer is hired. Birthday parties result in too many birthday cakes, as that's all the caterer makes. Face/palm. Best of luck.

Yes, I found it!  Thank you!

Unfortunately, I didn't find it on time and the engagement party flopped.  Partly because I have little or no experience of planning these events.  But my sims got married and invited two of the same guests to their tiny apartment and they left on their honeymoon soon after!