Not sure if it is a hobby, or even unusual, although I don't know many people who do this in the way I do.
I also didn't realize I had been doing it for so long.
About 20 years ago, I started approaching individuals, manufacturers, and groups, to donate "Items Useful To The Infantry Soldier", which I in turn ship off to my former team, when they deploy. The team in it's current configuration is a Scout/Sniper platoon for the 1/327 Infantry, 101st Airborne, Div. In my era (VN) they were called Tiger Force. The team, since meeting a bunch of us veterans of the group, back in year 2000, have taken up the name again.
Most of our elder Vets, Organized by me, donate something to the cause, whether it be a few bucks, or hand made items such as wool socks or hats, to micro-tools, and multi-tools. We've even sent a periscope the year they were working mostly urban areas in Iraq. I have gotten corporations to donate, as well, Spenco sends us foot care products, especially the thin "moleskin" type product they make, and Stiletto tools sent us a collection of Titanium tools, for entry, such as pry bars, and hammers, during the Iraq deployments.
I obtain compact binoculars, and compasses, silicon impregnated cloth, bore snakes, and small flashlights, and am always keeping an eye out for other small items. My basic search mode, is "what would I have really been glad to have in my pocket or ruck, when I was in the field, carrying everything, far from support". Handy items, small or compact items, etc. Of course, way before the Cigar thing became an organized thing, I was sending cigars to the team.
Summer deployments get cooling towels, winter deployments get gloves, plus each gets all that other crap as well.
I have developed a simple method to get people to help out: if they send me cash (I don't solicit cash, but some of my old team mates just say "buy what you think they need" I spend every cent on items, and pay for the shipping myself, If they send items to me, I pay for shipping to the APO, myself, and if they wish (which I highly encourage, they can ship directly to the team, once I have an APO.
I never reveal where the guys are going or when, but as soon as the APO is given, I pass that on, mostly to my team mates.
Several years ago, a member of this forum was most generous with a direct donation of heavy sweaters or jackets (I don't remember which). I was absolutely floored.
Of all my hobbies, interests and involvements, this gives the most satisfaction, and fulfillment.
I am a birder, hiker, back packer, rock climber, shooter, hunter, fisherman, recumbent trike rider, vegetable gardener, HAM, and rock hound. All of those have given way in some aspects to age, ability, interest, and/or money, but this personal project continues from year to year, seeking, gathering, soliciting, and making new friends of the current active duty team.
I have followed the careers of many of these young guys, some of whom are now elders themselves. Many have gone on to Ranger school, or SF selection, some have become 1st Sergeants and some CSM's, Many have retired or ETS'd, and most have created families, and worthy lives. We lost 5 during this period, and that hurt as bad as losing one during our own time.
When one of our young members was severely burned in 2007, I spent 3 months at his bedside helping him learn to walk again, changing his dressings, and going to PT with him. I reported daily to the other members his progress. We became fast friends, with his mom, and family, and with him as well.
This has been a rewarding, fulfilling and amazing unusual personal project.