It could be anything besides the obvious “I have yoyos in my yoyo case to make it complete”. It could be… types of strings, bearing types, a certain special yoyo? Let me know what makes your yoyo case feel complete.
For me I always have to have some extra bearings, a string cutter, extra Big Yoyo String stickers, a bearing remover tool, and my case must have as many stickers stuck to the upside to be complete! 
Your turn, What makes your yoyo case feel complete?
scissors or something that cut strings. I’m sure I look brilliant trying to chew off extra string because I don’t have anything sharp.
Egg-Crate Foam.
And some strings, bearings, and of course, yoyos.
I figure a string cutter and bearing removal tool to be among the most important. Well, string of course as well.
My String ball, hehe.
Mine isnt complete without a KILLER bearing and a new string fresh from the pouch…
nothing in the yoyo world feels better than that…
My yoyo case isn’t complete without foam
but in all reality my case isn’t complete without my bearings,strings, and a SD flow
A Peak and YYJ Hex
A Square Wheels yoyo.
A YYF Multi-tool.
And mine’s gone missing. 
My case is incomplete!!!
A big bundle of string.
My case is incomplete. There is a Moonwalker space begging to be filled Outside of that my case/pocket/hand has to have a Stealth Ogre in it. At all times.
My yoyo case isnt complete without a HUGE pocket full of stickers!
I don’t know why but I always have to have sewing machine oil and paper towels to wipe off extra lube if I overrule it.
…a Peak but now it’s complete. 
My Peak.
Yoyo glove
Actually, I get irritated when I can’t find my bearing removal tool. So, my case is never complete without a udsto7hifae7wry7weyhwr7er97reyrew79qx7e bearing removal tool.
Foam
My case isn’t complete until it’s been taken to a meet and the yoyos shared and enjoyed by others. There’s no point in having a case and filling it with yoyos if you don’t intend to take it out and share!