A bit late for this thread, but wanted to post my experience having just come back from a 1-week trip to NYC.
With the exchange rate the way it is post-Brexit, it wasn't very good for shopping. In terms of clothes I only bought one dress and one top from a US-only brand (Cuyana - they have lovely silk clothes and leather bags, not cheap but a decent price for the quality).
I wouldn't go to an outlet store if you are looking for quality clothing - most outlet stores have already admitted that the items they sell are made with cheaper fabric and stitching compared to the usual branded products. So basically you would be paying for the brand, but without the quality associated with it.
As for beauty, Sephora, which previously was a favourite of mine, wasn't that attractive this time. About 75% of the stuff there is also available in the UK for better prices with the current exchange rate. The other 25% are the Sephora-exclusive or US-only brands (Tarte, Sephora Collection, some skincare brands like Kate Sommerville, etc.). There were some interesting things but nothing that really caught my eye, apart from a small skincare set from a new brand called Farmacy. Some of the other sets with mini-sized products were actually good value, as is the Sephora brand, but I ended up not getting much. I also went to Sak's and Bergdorf Goodman, but hated the experience as you can't really browse the counters in peace, the staff will come to you asking you lots of questions, which is a bit intimidating if you just want to browse. Made me miss the UK counters where staff usually leaves me to browse as much as I want! I don't blame the US staff at all, it's just their culture of customer service that isn't my cup of tea.
Beauty products at the drugstore seemed much more expensive than when I was last in the US (6 years ago) and were not such a bargain, but I was able to get some good deals like buy one, get one free for Revlon and Almay products at CVS. The brands that are sold in the UK, like Revlon, Maybelline, L'Oreal, etc. have different products and a wider selection of shades than they do in the UK. I got enough lipsticks and lip balm to last me for the next 20 years
The prices for drugstore products don't seem to be the same across the board, so it's good to shop around and check the prices online before buying drugstore makeup or skincare. Most of the deals require a store card, which you can only do if you have a US address and phone number. Because I was only staying for a week, the cashiers usually asked another customer in the queue to let me swipe their card, which they did - so I got the discount and they got the store points.
Ricky's NYC is also a good place to go, it's a beauty supply store mostly geared towards hair products and tools, though they also have some makeup and skincare. They often have quite a few good products on clearance for more than 50% off when they decide to stop carrying a certain brand. I got a great Japanese hair oil that I had been eyeing on eBay for les than half of the eBay price.
As for other stuff, I found food really expensive compared to the UK, particularly in the supermarkets, though I must admit I only went to the upmarket grocery stores like Whole Foods (which are expensive here too) as they were nearer where I stayed and more convenient.
Magazines are not worth the cover price. Most of them are available on iTunes for much cheaper, even if you don't buy a subscription.
Museum tickets are also quite pricey, but most have a day a week (or a month) when they do "pay what you wish".
Apart from the bad exchange rate, it's still a wonderful place to go, and I hope yo be back soon!