"Who the hell are you?"
Technically, it's one first adventure. At least for him.
He feels a little bad that it takes him this long to think of it (although really, for the plan he has in mind it's all the better). Somewhere in between his first kiss with River and realizing that he's more head-over-heels than usual for (and possibly married to) a woman whose timeline runs roughly backwards to his, it occurs to him.
Time is, after all, both wibbly and wobbly. And occasionally wimey.
It's such a narrow gap, and he has to find it while not thinking too hard. There were days in there, between the him-that-wasn't-the-Doctor and the him-that-was-again, that he doesn't remember too clearly. Days he's tried really hard not to remember too clearly, if he's honest with himself, and this sort of thing is exactly why he rarely is. But there they are, blurry and better not thought about, and if he can just keep from thinking about them a little while longer, he can make this work.
"Who the hell are you?"
"It's going to be all right."
It takes him a long time to find a place and a time, hampered as he is. That him had been so jealous of Rose, hoarding her moments close to him, unwilling to let her slip through his fingers. How he'd watched her with Mickey (and, briefly, Adam)! How he'd watched her - and now it's frustrating, because there is so little of Rose's time unaccounted for. Her time in this universe, so very brief, parcelled out so carefully; he knows so much of it already, so little left to change.
Still some, though. Enough for one last present to himself. Merry Christmas, Happy New Year, and all that. This will have to be enough of Rose Tyler to last him for all the holidays in all of forever.
"Who the hell are you?"
"It's going to be all right."
"No it won't. What do you know?"
It's even harder to make it work without hurting her, and hurting Rose Tyler is Never Acceptable. He can't let her see his new face, can't let her guess at the future - those are secrets he can't ask her to keep, not from him. Too much to carry, too heavy a burden.
(He would carry all her burdens, if he could.)
In the end, it has to be a note. He wouldn't have minded One Last Time for himself, either, but him being happy has never been as important as not hurting Rose. So a note it is, in his best approximation of a handwriting he forgot how to write two hands ago (well, four hands, or five, depending on how you count) giving her a place and a time and the most important instruction of all: don't tell. Don't ever tell, Rose, this is important, not even me, not even if I ask (he doesn't remember asking, but he's playing fast and loose with spacetime, so a little extra cautiousness might come in handy).
He leaves it on her dresser, together with a vortex manipulator set to take her to one place and one place only. A round-trip ticket.
Place: the Tardis.
Time: the days he's forgotten.
"Who the hell are you?"
"It's going to be all right."
"No it won't. What do you know?"
"I'm the Bad Wolf. I know all sorts of things."
"Well, isn't that fantastic."