First, I’d recommend packing a few extra golf balls. When you travel abroad, golf balls can be very expensive and your favorite may not be available. Secondly, whether abroad or not, not knowing the courses you will likely lose more balls than usual, even if you do play well. I’ve often witnessed both experienced golfers and fellow golf writers frequently run out of balls, which can ruin the golf experience.
Secondly, I always take a couple of plastic baggies for gloves (have a spare), balls, sun lotion, cap, band aids, lip gloss, aspirin, band aids, etc. along with a pair of golf shoes in your carry-on luggage. Whether you rent clubs or in case your clubs are mis-routed, you’re still in luck. And by packing in baggies, should you encounter bad weather, your equipment will stay dry once you store them in your golf bag. Speaking of keeping dry, those lady’s shower caps you find in the hotels work great for protecting your favorite hat.
Finally, I recommend that you pack two large trash bags on the top and bottom within your luggage, especially if the material is canvas or the like. Bags sitting outside in the rain waiting to get loaded can get soaked. Using these plastic bags as liners, the insides are not affected. Once on the course, should you encounter really cold or wet weather, simply poke holes in your trash bag for your head and arms and wear it, or you can place one of the bags over your golf clubs/bag to protect them from the rain. On your way home, those same bags may be useful for storing your dirty clothes or packing liquid refreshments so as to guard against breakage.
One postscript: should you have any particular valuable or precious equipment, consider never taking any that is irreplaceable on casual trips. Breakage, theft, and the like can and unfortunately does happen. I learned that lesson very dearly once with premium classic clubs which also happened to be my “tournament” ones. Though they looked old, they were worth several thousand dollars and even more valuable to my game. Our domestic airlines permanently lost them before I got to my destination. Now that precious putter or wedge stays home.
