My focus for birding is Australia and its territories. When I travel overseas, I always keep a record of what birds I find and I often will include a few days during the trip when I go to some places which seem prospective for finding birds. In the past, many of my overseas trips were work-related. With those, if I was lucky I might have manage to get one day of a weekend when I could go birding. Now, the majority of my overseas trips are with my wife, and are aimed at general tourism but with me ducking off some times. I've also done some trips to Japan, focused on visiting sites for Grey-tailed Tattlers.
Although I don't formally keep a world bird list, I do have a reasonably good idea of what I've seen before and what are new species for me! And, I am working (slowly) on pulling together my world list. Unfortuanetly, things like eBird weren't around for most of my birding years and so all of my records are buried in notebooks.
Here is a link to a file summarising my “recent” trips (those from 2006 onwards; my record-keeping prior to that was patchy). NB short trips involving less than a week away are ignored: