No-Skill-Guitar:
Get a [guitar (Jasmine S35 Acoustic Guitar)] + [chord buddy (chordbuddy.com)] + [electronic tuner (Intelli IMT500)]. Any time you hear a good song, look up the chords for free on ultimate-guitar.com, save the page as a .pdf, and you'll be able to play the song right away on the guitar with the chordbuddy, even if you don't know how to play the guitar. You'll bond over sing alongs, and you'll be learning how to play the guitar at the same time with the help of the chordbuddy.

Hacky sack

Local Multiplayer Games (everyone plays on the same computer):
Get a couple wireless controllers (Microsoft Xbox 360 Wireless Controller for Windows), and download these local multiplayer games from Steam:
1) Speed Runners (http://store.steampowered.com/app/207140/)
2) Starwhal (http://store.steampowered.com/app/263020/)
3) Duck Game (http://store.steampowered.com/app/312530/)
4) Nidhogg (http://store.steampowered.com/app/94400/)

Naptime:
Get an ENO hammock for people to nap in. It's healthier and easier to sleep in than a real bed, and can be stowed away. They'll be able to work later.

Have fun

Do you have weights or a treadmill? One of things my friends who work from home or have start up software companies really benefit from is being able to have a physical release after working on a computer for so long. Tony Robbins says that our physical state needs to match our mental state. Being able to work yourself up physically will make working a lot easier, because your physical stasis aligns with the intensity of a lot of the mental work.
At Naughty Dog and Microsoft here in LA they have a gym, a yoga studio, and resting space so that they can physically align with whatever kind of work they're doing.

I agree with competitive multiplayer games. Those are great fun ways to get people hyped. Things like Fifa are great and FPS games are really exciting when you know the people you play them with. Tekken is a great game for two people to take their day out on.

ONE LAST THING. TEA, a friend I made who works at Naughty Dogg as a higher up and he swears by tea, it's incredibly cultural, there are different blends for different moods. A lot of people get behind it as an alternative to coffee or magnesium, and as hobby learning about all the different types is fun. And when done well it can be a very communal experience with whoever is serving the tea almost as a bartender where he can give you a blend to feel focused, hyped, relaxed, or whatever you need to get your job done.

Hope I helped in some way :)

I'm a big fan of board games and Card Games in general. We play board games as a team almost every Friday. Some of my favorites are Survive, Star Wars Armada, Takenoko and Sushi Go. Star Wars Armada in particular was super fun and super geeky - which we like. Great question and smart thing to think about...

A bin of Legos or wooden blocks is an inexpensive, portable way to give people something to do with their hands while they're in a meeting, or on the phone. Having them out in a public area will organically lead to collaborative building projects and creative thinking.