I disagree. I did chins with 90 pounds around my 15 inch neck in high school and got on just fine.
Seriously OP, listen. Treat them like any other lift. You wouldn't try to get good at benching by going to failure twice a day with the same weight, why would you do it with chinups? Ramp up to a top set, vary weights and rep ranges, let them rest as much as they need then hit them again. Hell, I've used the 5/3/1 template on them with some success and now do something pretty similar.
A laptop bag full of rocks can be fine per se, but you'll want to be able to add more weight. I'd recommend joining a gym. If you don't want to do that, buy an olympic barbell, more weight than you can deadlift, 2 oly db handles and lift at home. Weights last forever and make it way easier to manipulate weight for chinups. They're also the answer if you want to be considered very strong.
Dip belts are nice. If you're too cheap, rope/chain and a carabiner works very well.
Also, read this: It will break some mental barriers concerning weighted chins.