We use Krill oil here. We are just starting to use the new product at Costco...their brand, of extra strength Krill oil. Their brands of supplements have been high quality in the past and I think this one is too. But for years we have been using MegaRed which Costco has affordably and often a coupon in the monthly mail.

There are many good fish oils... here is a evaluation as to content and quality/price:
https://labdoor.com/rankings/fish-oil

Most fish oils (excluding krill) are processed by central large factories, so they tend to be of better quality now than in the past. Nordic is popular and Carlson's... they are well established brands. NatureMade is a good company too, and more easily found in stores. The oil is best absorbed with food...so take with a meal.

No I don't know about improved versions of NAC or AlCar.
NOW brand is good and affordable. So is Doctor's Best.
Acetyl carnitine is not well absorbed so divide up doses if you take in gram quanitities, throughout the day.