3 day old? That sounds real young. Is it weaned from its mother yet? If not, you best plan on feeding it. You will have to actually feed it then.
Litter box is simple. Just put them in, and scratch it a few times. Every cat I ever had hit upon this right away. (I have had over a dozen so far.) Just be sure to clean it regularly. Depending on the size of the litter box compared to your cat, you might get away with just scooping it every day. But even if you do that, make sure to change litter at least once a week. I would recomend at least twice a week. (Lets face it, would you want to use your bathroom if you couldn't flush but once a week? 😛)
As for food: Go the extra mile and get good food for him/her. It will save you trouble in the long run. (And expensive vet bills.) Science diet is a good brand. Also, look for low/no ash content. Ash causes urinary problems in cats - particularly males.
Look into getting the cat spade or neutered. No I am not big on this, but it helps both of you in the long run. You really do not want a male cat marking everything. :disgust:
Declawing is optional. But it is something you should consider. Again, it isn't one of my favorite things... ... But do a little research on it. There are two procedures I know about. One, they just remove the claws. Simple, and comparatively painless. But it will have to be repeated. The other, the vet breaks the knuckles. This really bums me out. But it may be the only way to deal with your cat if they get into clawing up your furniture. Also, every vet worth their salt will tell you that you only need to declaw the front. This is correct. If your vet tells you otherwise, go somewhere else.
As for toys. Shoe boxes, and crumpled up papers should be good for you for a long time. Also keep an eye on your small items. (Candy, pills, watches, etc.) Some cats just love to get into this stuff. In the future you might get into buying things specificly for the cat. WATCH OUT FOR TOYS WITH LITTLE ITEMS THAT CAN COME OFF!!! Like little fuzz ball noses and such. If it comes off, and the cat swallows it, the cat will die. I have had a cat die this way. No fun. Also, look out for getting the "Jingles Balls." Not so much a health hazard for your cat, but for you. 😛 These are plastic ball "cages" with a bell inside. Cats love them. But they have a habit of leaving them where you can step on them with your bare feet! 😀 (Kind of painful.) Cat nip is a must, but I recomend waiting a few years to introduce your cat to it. And if you can swing it, actually growing cat nip is the best. (It smells kind of like peppermint when it is fresh.)
The rest is pretty much common sense. The better you treat your cat in the early months, the better it will treat you for your whole lives.
Enjoy! 🙂