Fisher-Price Healthy Care Booster Seat
You can buy a full high chair set-up, but I prefer the portable, adjustable Fisher Price Booster. It straps right into your kitchen chairs and you can take it with you on the road or out to the restaurant. It also adjusts in height from first eaters through toddlers.
I have friends with twins who swear by these booster seats - they travel easily because they fold down, turn any chair into a high chair, can be used as a seat on the floor, and the trays are removable and dishwasher safe. Perfect for home, travel, going out to visit friends or grandma's house.