I was going to say a tablet to document my journey with... but yeah, definitely a towel.
.
If you can hitchhike the length and breadth of the galaxy and still know where your towel is, you're a hoopy frood to be reckoned with.
My version of Rose Tyler. Be they male or female, human or alien, I'd bring the one who is my closest friend, and the one that I love the most. Though I don't know who they are yet, sadly...
If this include s nonexistent things, then a book that I could turn into any book I wanted. And if I didn't know if the book, I'd give it a rough description of what I wanted and it'd give me recommendations.
.
If you can hitchhike the length and breadth of the galaxy and still know where your towel is, you're a hoopy frood to be reckoned with.
In that case: a big ol' coat