I'm a marathon runner and we do not carry water bottles, we are handed them along the way and toss them aside after guzzling the water. Our bib number is our ID, some do carry a dog tag type ID or medical ID. Most do not use music/ear buds. We need to hear the approaching runners. Many people do not have a team of support people to with them to hold their stuff. With that being said, I suggest a small quilted tote bag with some lotion, water, protein bar and soft socks, and any other goodies your friend likes. Give it to her a few days before the race and wish her the best.