Can't really think of anything that I really regret not doing as in contrast to most posters on here, I've had the likes of Deltics on the mainline, first gen units (101,105 etc) as well as 20s,25s,31s,33s,37s,40s,45s,50s,73s on the main line. Of the locos/units seen the ones that got away that would have been nice were the Calder Valley 110s and the Trans Pennine units. By the time I got to Scotland, the 26s and 27s had gone - would have liked them. Other than that I remain pretty satisfied with the stuff I've had in the UK and Ireland