>What other struggles are there that we can take on to facilitate bonding?

I've found that competitive gaming has been pretty good for this, with the stipulation that it mainly applies to 1v1 games which are usually played at live events (such as fighting games like Street Fighter and Super Smash Bros Melee, or card games like Magic: The Gathering), rather than games which tend to have more of an online presence (MOBAs like League of Legends and digital card games like Hearthstone are less good for this). Pretty much any game that has an active local scene will have at least one local business (usually a game store or an arcade) that runs weekly events for a nominal entry fee.

The immediate benefit to playing a competitive game that has an active local scene is that you'll find yourself in the same space and spending time with the same group of people for several hours at a time on a weekly basis, so at the very least you'll become acquainted with most of the locals. Attend enough of these weekly events and it's usually pretty easy to get plugged in with people who run smaller, less-official events on the other days of the week. One of the things I like about Magic: The Gathering is that I can move to any major city, go to a Friday Night Magic event, and quickly get plugged into a local network of people who share my interests.

If you ever take your game beyond the local level, then you'll also probably end up forming more social connections with people in the local scene, as traveling to events becomes much more economical when you do it with a group of people to split the cost of hotel room and gas. When you travel to an event with a group, you end up spending a lot of time with the same group of 3-4 people over a period of a weekend, which can be a great bonding experience. There's also the fact that traveling to events like this has the effect of making you feel like you're competing together as a "team," even if you're all competing individually; it's fun to root for people from your own city, and it's these sorts of experiences that really offer the kind of "struggle" that I think is good for facilitating bonding. Part of the benefit of traveling to an event as a group is having people to commiserate with after you get knocked out of the tournament.

The "commiserate with and/or root for people I recognize from my own city" can also apply to people you didn't travel with, and in fact having serendipitous encounters with people you know but didn't travel with can also be a great bonding experience. When you drive four hours to an event and then see someone you recognize from home, it can make for a great, "Hey, good to see us!" moment, and even if it's not someone you know really well, you always have "so how's your tournament run going?" as an icebreaker. These moments can often end in making dinner plans where you get all of the dozen or so people from your home city to meet up at a bar or diner, and a lot of the most memorable experiences I have from competitive gaming come from those late-night dinners.

I've found that any hobby that offers "casual regular events on a weekly basis, plus occasional group trips for the people who take it more seriously" is a great recipe for bonding; I played competitive Pokemon for several years despite not enjoying the game particularly simply because of the great social experiences that I had with playing it. I have friends who are into cosplay and anime conventions who have had analogous experiences. Competitive gaming is the main one that I engage in that I consider "strictly recreational," but I've also had some similar experiences with the local game dev scene and with local writing groups, which are adjacent to my professional life. Some of my favorite experiences in game development have come from going to a big event like PAX and just having friends (both from internet and from back home) stop by my booth to chat. There's just something great about traveling across the country to an unfamiliar city and seeing a familiar face that I find really special, and events like these can also be a great chance to turn "internet friends" into "real friends."