I think you have the basics – crate, food and water bowl, collar, id tags, leash, toothbrush, ear cleaner, shampoo, tons and tons of toys, bed, travel crate, seat belt, flea treatment, training treats, bully sticks etc.
The collar/leash/harness type depends on what size of dog you’re getting. For our GSD puppy, we have a flat collar with tags, a prong collar for training, a body harness, an auto harness, a seat belt, and a gentle leader. Even with all that, I think we’re going to order a martingale collar as well.
Surprisingly, we’ve used all of them at one point or another for different stages. When she was small (20 lbs) we used the body harness. Now that she’s older we use the prong collar for 10-15 minute training sessions and the gentle leader for walks. She used a travel crate in the beginning when she got car sick but now uses an auto harness and seat belt. We’re hoping to eliminate the gentle leader and prong collar with a martingale in the future. For a small breed dog you might only use a body harness, flat collar and car seat of some sort.
We bathe our puppies a lot since they get filthy playing together. We have a good oatmeal shampoo, ear cleaner and we brush their teeth with a doggy toothbrush when they get bathed. We’d do it daily but their raw diet really eliminates the need to.
Now that they’re potty trained, they have a bed in their crate and a bed outside their crate for sitting with us. We wouldn’t recommend potty pads, though each person does things differently, and we didn’t want them to learn that it was EVER okay to potty in the house, regardless of where they did it.
Our trainer also had us regularly tether the pups so a second leash or lead for tethering might be a good idea. If you’re tethering them to something like a couch it can be a pain in the butt to pick it up everytime you need the leash.
Then you have your small army of puppy toys so they have way too many things to play with so they never turn to your stuff for entertainment. The indestuctible ones are nice but probably won’t work with a small breed dog since they’re really hard. We use Zukes salmon treats since they’re a good size for a training treat (we break them up even smaller, into halves or thirds) and give them either a bully stick or long stuffed with something to keep them occupied in their crates.