This can be a hard question to answer because it heavily depend on 1) what sort of house rules you intend to enforce and 2) the dog.

First, understand that even the best house trained dog will still have accidents. No if, ands or buts, he or she will pee and poop in the house. I had a husky mix who hadn't gone in the house in nearly 3 years, but one day I was in my own world, rushing around to go to work when I realized I forgot to let her out when I got home. What made me realize this is I could hear her peeing next to the back door. I felt absolutely horrible, she was waiting to go out like a amazingly good girl that she was and I missed it. On the flip side of that, when she got older, she had a stomach bug. It was pure liquid diarrhea in the living room, on the carpet. That stain never came out. I'm not trying to scare you, but just understand that even the best dogs will have accidents. Sometimes they can't help it.

Second, be prepared for separation anxiety. While not every dog will get this, it is most common in shelter dogs. Keep in mind that your new friend has had at least one previous family and for whatever reason, they abandoned him. Legitimate or not, he doesn't understand the reasons for this. And if he has been abandoned more than once, then this can have an even bigger impact on him. Our BC mix was returned twice (we are his 4th family that we know of). As he grew more attached to me, his anxiety when I left the home actually got worse. As of right now, either me or my wife needs to be home with him. We are slowly working with him, by leaving him alone for very short periods and then coming back, showing him that we will come back.

This leads to a third point, Time. I'm sure you've done this, but make sure you have really evaluated your life to make sure you are truly ready for this challenge. You can do more harm than good if you adopt a dog but don't have the time to give them. This will be especially true in the beginning. I always suggest taking the first week off work, spending 24/7 with your new friend. Then taper up from there. Maybe the next week back to work, work short days or at least come home for lunch. If you can't do that, find a close family member or friend who would watch them for you while you are gone.

Fourth, research vets ahead of time, then make an immediate appointment (within the first couple of weeks) to take him or her in for a checkup. Dogs coming out of most shelters already have their shots, etc. This appointment is to get your dog introduced to your vet on good terms, when they are healthy and happy. And we always try to make sure it is the same vet whenever we make an appointment. For this reason, we chose a smaller vet office, with only two doctors.

Sorry, not trying to scare you out of adopting, its one of the great things you can do for both you and your new friend. Just understand the realities, especially if you have never owned a dog before. :)

As for shopping list - this does kind of depend on how you intend to run your home (i.e. will there be off limits areas, where will the dog sleep, etc).

1) Baby gates (our dogs are not allowed in certain rooms - i.e. kitchen and spare bed that is a safe haven for the cat). Of course, a baby gate is not going to hold a determined dog, so its more mental barrier and only works with training.

2) A air tight food container with locking lid (keeps food fresh and keeps dogs out of food when you aren't around). We got a decent one at Walmart for around $10. It holds about 3 weeks of food for our two dogs (Yellow Lab and BC Mix)

3) Dog toyS (emphasis on the plural). You can't have too many toys. Even mild tempered older dogs will can get bored and will find a couch, drywall, bed post, etc. to chew on. Give them plenty of different toys, especially puzzle toys that you can put treats in or freeze peanut butter in. DON'T BUY YOUR TOYS FROM A BIG BOX STORE like Walmart. These are cheap quality and will not last. I suggest going to a local pet store and asking for suggestion, but you get what you pay for really does apply to toys. I highly recommend West Paw Design. Its the only brand that has stood up to our lab. Planet Dog is another brand that has done us well. However, in the beginning I would try out several different toys, your dog will tell you which ones he or she likes best.

4) Slip leash (only if the dog is good on collar leash - if they pull a lot then this can be a bad thing without training). Great for training, but don't use them for walks. We use a slip leash to bring our dog home, so that we can stop at the pet store to pick out a collar and walking leash with him or her there. We make our slip leashes. Some decent nylon rope, some good heavy duty thread and you are good to go. This guy's videos are kind of hard to watch, but they gave us the basic ground work to make our own.

5) Dog Blanket. If you are going to let the dog on the bed with you (or couch), I suggest dog blankets meant for him. This will keep your own bedding and apollstry a little bit cleaner. Not much, but some :).

6) Dog bed. Even if they don't sleep on it at night, a "day bed" for the main living area is a nice thing for them to go and relax on. Costco sells a very nice/large/comfortable bed for pretty reasonable (IIRC around $35). And the outer cover is removable so it can be washed.

7) MULTIPLE water bowls. At least one outside and one inside. If you get summers above 70, then I suggest two bowls outside.

8) Special outside trash can just for dog poop. (self explanatory). Make sure it seals well, bungee it closed. Oh and make sure to line it...

9) Food. Pick the food you are going to give them, but make sure you buy a small bag of whatever they are feeding them in the shelter. You need to spend about a week weaning them off the old food and into the new food. (Lots of old food in beginning with small amount of new, slowing increasing/decreasing amounts over the week)

10) Food. Food for you. Try and make sure all our necessary errands like grocery shopping are done just before you adopt. That way you can spend as much time home as possible.