Well, two kids in and I can safely say that I have figured out what the most useful item I have purchased for the money is. Our booster seat.
We bought ours a few years ago, so I think it was only around $20 then, but even now it's only about $26-30 (depending where you buy it). This seat has been a life saver for when we are out and about and on trips (ones that we don't have to travel by plane to). At home we use it for a high chair for the younger baby, and a booster seat for Kayla so she can reach the table and eat with us.
It folds up, making it very easy to take with you. We have brought it down to Chris' office for work parties, to friends' houses for dinner parties, to my grandma's house for lunch or dinner with the family when they all come to town, and on our travels around CA. It's easy to clean and very sturdy. Unlike some other slightly cheaper booster seats, the straps are well-made and don't loosen by themselves (making you frightened that your child will rock the seat right off the chair you have attached it to).
It has three tray positions for your growing child and the bottom of the seat can be adjusted taller or shorter depending on your needs. We currently use it in the highest position as a booster seat so that Kayla can join us at the big table. She loves it. No more tray, but we can still strap her in if need be(though usually she's well-behaved enough that we don't have to). The tray is large enough to fit a small plate on for the time when you are practicing using a plate, but they aren't quite ready for the table yet. It's just a fantastic buy for your money.
To save a little money (and because I assumed most of those types of seats would be about the same), I bought a cheaper booster seat for Elise, and it has not been a pleasant experience. I hate to feel like I wasted money, but since we've got another one on the way and the fisher price seat is ACTUALLY 100% useful, I think I may very well get rid of the crappy one I bought, and invest in another Healthy Care Deluxe Booster Seat.
On a side note that is slightly related....Elise has learned another word: "good". We always ask Kayla how her food is at meal times, and her response is usually "Good!". We usually ask Elise too, and the other day she answered with a resounding "Goo!" She even answers for Kayla sometimes now too.