I'm sorry if a lot of this has already been said, it's hard to keep track.
We use nappy bags, far cheaper than dog bags.
Would definitely recommend a harness for walks and for the car if you're not using a crate. We use a step in one for puppies and K9 for adult dogs. They're brilliant.
Dogs have to be secured in the car so we use a bungee type attachment that we got from amazon. They clip onto rings in the boot or into seat belt clips in the back.
Chew toys you can put in the freezer for teething.
Think about what you'll do at night/when you're out. Even if you don't plan to use a crate long term, they're brilliant when toilet training/through the chewing stage and helps with separation anxiety. Good for holidays too.
We use a long retractable lead for walks but also have a fabric/leather lead with a handle that can easily be looped round table legs in pubs and on picnics. It's so handy to be able to eat your lunch without having to hold the dog lead.
Tic remover is essential
Some pet wipes or good microfibre cloth for cleaning round mucky faces, ears and eyes.
Good set of brushes suitable for your breeds coat. I like Oster.
Do lots of research about how to feed, what they're eating at the moment isn't necessarily the best thing. I find kibble and tinned food means stinky and loose poo. There are some really good dry foods now but some of it is absolute shit.
Lots of vets offer a monthly care plan which will include vaccinations, flea and wormer treatment and often other stuff like nail clipping and health checks.
Do your research on insurance, sign up for a free trial with Which. There's a vast difference in prices and types of cover.
Is it for life or annual cover?
Does it cover dental as many don't?
How much excess will you pay?
Do they stop cover over 9 yrs?
Sorry that was an essay but we have learned a lot over the years mostly by ballsing up ourselves.