Ninety-nine activities on this site, ten Slayer masters and twenty-three skills, and only one evening. The randomizer puts the ones you would actually be happy to get onto a wheel, weighted however you like, and spins it.
Anything else an evening looks like goes on too — sort the bank, finish a quest, a boss whose drop table nobody has extracted — as an entry you type in yourself. Any entry can keep its own amount range, because five to twenty-five Zulrah is an evening and five to twenty-five of something else is a fortnight.
Packs turn on wholesale and then you take out what you do not fancy. Load a username and anything above your levels drops out: requirements come from the Slayer data, which states them for the bosses and the masters. Nothing else on the site states a requirement, so nothing else is locked — it is left open rather than guessed at.
It can roll how much, as well as what: fourteen Zulrah kills, three Barrows chests, 312,000 Woodcutting experience. One range covers everything and is meant to be changed — the site knows how long a kill takes for about a fifth of what is on the wheel, so a default that was right for those and invented for the rest would be worse than one that is plainly a starting point.
The last few results stay out of the running, so a short wheel still moves around instead of handing you the same boss three times. What it lands on can be taken off the wheel, which is how you work through a list rather than just roll a die at it.