The tackle box we use (have had it about 15 years) has adjustable little square boxes on the top “shelf”, and a large open area under the lift out shelf. The only problem I ever had with it, was that I kind of wanted to have a different set of studs in each little box --you know, a “complete set” --but I don’t know that that many studs exist. Even so, any time I saw a different kind, I’d buy 4 or 8 to add to my collection. In all honesty, the event horses used pretty much the same style studs unless the ground was unusual —hard clay or deep, deep turf might make me pull out something different. I always wanted to use the mud studs, but when the footing was that horrible, the CC was rescheduled for a subsequent day.
I did discover (and this was as I said, 15 or so years ago) that there is a bit of art to selecting studs, more than an exact answer. Since I was always the groom and never the rider, studs were my job (daughter rode, and had left the stud decision to me). I truly enjoyed sitting with the other grooms (some groomed for big-name riders!!) and chatting about which studs to use —occasionally --the big name riders would pull up a hay bale and join the discussion —Bruce Davidson was one who did, and I think Dorothy Crowel? but might have been Cathy Wieschhoff --were a couple that did join the discussion --usually during a rain delay as we went back and forth about this stud or that —I mostly just listened and asked questions because I was just a mom --but seems like the more renowned the rider was, the nicer they were to “us grooms.”