D&D adventures, living out my favourite books, films and videogames, outdoorsy stuff (swimming, hiking, etc.) without pests, historical reenactments, and sex.
Hiking beautiful places in beautiful weather.
I will swiftly acquire the reputation for being the weirdo who refuses to go into the holodeck.
WOW.
Can I have your holodeck time?
As long as it’s feasible for me to use your taking such time to sabotage your career to my own betterment, sure. 
I’m not refusing the holodeck out of any sort of moral superiority. I just know myself well enough to know that I can’t be trusted not to overuse it, so I’ll deny myself access. I’m sure there’s holosuites I can use on Earth.
You can have my career. If there’s some way for me to just live in a holosuite, I’ll do that.
I mean, who’s to say it’s not real? It’s all the same to my brain.
I would definitely bring my “superheroines-in-peril” fantasies (as seen at my “Deviant Art” website : http://gytalf2000.deviantart.com/ – “Not Safe for Work!” ) to life!
Seeing Wonder Woman, or my heroines Panther Girl, the Polecat, and “Occulta, Witch of the Silvery Star”, getting knocked out, defeated, and captured by various villains, like the Dastardly Disruptor (who is my evil “cartooniverse counterpart”), would definitely be a ton of fun!
I’d bank my holo-hours and trade them to other crewpersons for real sex.
If I’m already getting sex, then it’s beach time every time.
If not, there’s a little bungalo nearby where the Milton twins await.
Anyone who abuses their holodeck privileges will be assigned holodeck cleanup duty.
Eeew!
I was just thinking that.
There’s got to be a mop and a bucket nearby.
What, no one wants to pretend to be a geek in the 21st century? It’s a fun time!
(I presume the holo-sex cleanup is done with precision phasers set to “disintigrate.”)
I’ll tell you what I’d do, man: two chicks at the same time, man.
Nope, like everything else on the holodeck, its atoms are just rearranged to become other stuff.
Think about that the next time you request earl gray, hot.
Me too. A walk in the woods. Need a little green. And wind in my hair.
Also, very occasionally, silly romance novel-type stuff. Not sex. That would be weird, I think. But Romance Novel Guy could try to persuade me!
And maybe the occasional trip to a five-star restaurant. Could you taste the food? Could you eat whatever you wanted without any aftereffects? Okay then!
And the occasional trip to the great museums, great points of interest of the quadrant/galaxy/whatever.
I have long thought that a Holodeck would be the ultimate martial arts training tool, simulating a classic sterotypical dojo/gladiatorial arena/basic training/etc.
I would be using my time in an interactive adventure designed to teach me martial arts, as well as live out my fantasies of carving out my own kingdom or something along those lines. Man that would be great.
I’d program the holodeck to take the fractions of a minute everybody else left unused at the end of their hour and send them to my account.
Just be careful about Professor Moriarty.
I wonder if there are any regulations governing holodeck use, besides the “no sexual fantasies with officers” rule on DS9. Could someone use the holodeck to, like, disembowel a holo-dude then strangle him with his own intestines? Because there are any number of gamers and torture porn fans who would masturbate themselves raw over that.
Point of order: Is the holodeck access limited by the number of holodecks, or by my own free time? If the former, then it’s probably a good idea to try to find a half-dozen or so like-minded folks so we could pool our time. That’d not only mean that we could spend more time hiking mountain trails or what-not each week, but it’d also provide some company on the hike.
Of course, I’d still keep some solo time on my schedule, for… various purposes.