Wow, I would NOT be thinking about sex during a zombie apocalypse.
When it takes all of my energy just to focus on survival, sex would be the last thing on my mind. I can't say that I've experienced a zombie apocalypse, but I've lived in a natural disaster zone, which is the closest scenario I can imagine in real life. And in the cases of most people desperately seeking for food and shelter, sex is not even a blip in their consciousness. Even if they've given up the fight, most of them are too exhausted to do much of anything, much less participate in something as energy-intensive as sex. Just my two cents.
Anyway...fan service for the ladies (manservice?). Well, as I've said before, I don't usually like the way fan service is used, so my tastes might moderate and tame compared to others. Shirtless scenes are pretty standard in Western media, some women like pantless scenes too. A cast of good-looking guys with a range of body types, from pretty boys to muscular men, helps in appealing to a wider base. Personally, I like a little bit of Ho Yay between the male characters, if not straight-up physical attraction. And of course, not all of this has to visual; a sexy voice and way of talking goes a long way as well.
If it helps any, aside from the face, "female gaze" tends to drift towards male abs, butts, arms/shoulders, and crotch. So fan service highlighting those areas might be more effective? Maybe? (I know this isn't true of all women, but it's true of many.)