Hats of course! They are small & fit in the suitcase, or, if the suitcase is full, put it on their head.
Here are two hats that I knit for my nephews who live in Denmark. They are both knit from the Heel Stitch Hat pattern by Purl Soho.
This hat is for my 9-month old nephew, Elvis. It was knit using Red Heart Soft Prints yarn in Waterscape on US-8 size circular and doublepoint needles. I used the baby size on the pattern.
The second hat is for my two-year old nephew, Jeremiah. It was knit using of Hobby Lobby I Love This Yarn! in High Sierra Stripe on US-8 size circular and doublepoint needles. I used the toddler size on the pattern.
On both hats, I added a pom pom which I purchased from Hobby Lobby. Two Christmas gifts done and they only took a couple of days each to make.