There is an art to packing for a three-year-old, a balance of parental authority and preschooler choice. It involves observation of your child to see which items are current favorites and might be missed as well as resignation to the fact that you will make some mistakes. My husband and I frequently travel with our daughter and have since she was very young and we still get that delicate balance wrong at times, as we did this morning. In many ways packing for an infant is easier. You need more items, including some large ones like a stroller and a portable crib, but the infant herself is not likely to gainsay your choices. The preschooler, on the other hand, is perfectly likely to pitch a fit over her outgrown purple sandals that have lately become her absolute favorites.
We typically start with clothing when we are packing. Clothing comes primarily under the heading of parental authority, since a three-year-old doesn't know what the weather is going to be like or what we may be doing. Since having a child we have found it best to plan to do laundry sometime during the trip, because packing enough clothing for a person who will likely require at least two outfits a day becomes unwieldy when the trip is over three days long. We do the primary selection of pajamas, underwear, socks, and daytime clothes, although we usually try to pick the items that have been recent favorites. This means sorting through laundry to find the ones she is picking out of her closet for herself. Then we add shoes, jackets, and bathing suits at our discretion.
Toys are more a matter of her choice. We limit as to volume by giving her a preschool sized roller bag to fill. We also keep an eye on what she chooses so that we know she has a few of her favorite comfort items and a few staples such as crayons and legos. We would prefer to veto noisy toys for our own sanity but if she picks something obnoxious we make sure it's only accessible in our hotel room so at least the rest of the traveling world isn't perturbed. We used to choose books together but now we have many favorites on our Kindle. That cuts down both the weight and the challenge of making choices.
My husband and I don't typically consult our daughter in the matter of snacks, although that would be a good opportunity for her to exercise choice. However, our daughter is one of those children who likes the same foods over and over again and so we don't bother asking. We know she's going to tell us graham crackers, applesauce, and goldfish so that's what we pack. We are also in charge of special items, such as sippy cups, a sleeping tent and a few blankets, her epi-pen and her personal hygeine items. Mostly the entire process works well, although her items typically make up more than half of the luggage we are bringing on any given trip. And we do have the occasional minor tempests over items that didn't make the cut.
That's ok. We try to use these moments as lessons in tolerating not having your own way and being flexible in finding other solutions. She can wear the pink sandals today and with a little distraction and a little comforting she'll be content. As she gets older we can expand the amount of choice she has, training her in both making decisions and accepting the consequences of those choices.