I think the answer to this question is "That functionality does not exist", but in case I'm missing something: I've created a homebrew magic item that has a once per day effect, but it's not a spell (short version: it's a pouch you draw things from, and once per day you can 'call your shot' and draw what you want out of it rather than rolling on a table).

Is there any way to attach a name or description to the charge, or will it simply be a free-floating clickable box on the player sheet that they'll have to remember tracks the once-a-day ability? 

Exactly what you expected "This functionality does not exist".

If you create a Magic Item with an expendable charge and a special feature that is associated with that charge then nothing will be “free-floating.” Both the checkbox and the special feature will be attached to the Magic item and appear nowhere else. There are many Magic Items that are coded with ”charges” to track features that are not attached to spells. For example:

Pearl of Power, Ring of Evasion, the various Bags of Tricks, Chime of Opening, Wand of Secrets, all of the Feather Tokens, and the vast majority of potions to name just a few.

Right, the charge(s) show up on the item, but simply as generic 'charges' with no way to label what they do, which is what I meant by 'free-floating'.

Quote from AntonSirius >>

Right, the charge(s) show up on the item, but simply as generic 'charges' with no way to label what they do, which is what I meant by 'free-floating'.

 But there is a way to labels whet they do. It’s called “the description.” You see, you type in what the Magic item does in the “Description” field, and that’s what indicates what the charges do. Just like every one of those Magic items I referenced earlier. (Like, I’m really not sure what the issue is.)

Your might want to work on that condescension, particularly when you don't seem to understand the question someone is actually asking.

Quote from AntonSirius >>

Your might want to work on that condescension, particularly when you don't seem to understand the question someone is actually asking.

 Alright, lemme rephrase. Even if you did attach a spell to that Magic item and have it require a charge, the system still wouldn’t “attach” the spell to the charge.

Do you mean when you look at the magic item on your character sheet, and it shows the charges, the little space underneath it where it lists the spell names…? That doesn’t mean those spells are attached to those charges. All that means is “these are some available Spells you can cast with this item, and this is how many charges it costs.” They’re not actually attached to the charges.

So maybe you want to work on that Snark when you don’t even know what you’re asking.