What can non uni educated/low income parents do to bridge the educational gap

Read, read, read with them. Encourage them to do their homework. Instil a belief that school and revision and homework are worthwhile. Talk to them about current affairs, politics. Keep them away from social media and video games as long as you can. Limit the number of hours a day the TV is on. Encourage critical thinking, ask them why they hold a certain belief, challenge it and show them how to see two sides of a debate.

Be interested, support them in learning. BUY THEM BOOKS. Some of the most academically challenged kids I've taught have been ones where I've asked them to bring in a book from home and they've said "We don't have ANY books at home!" Get them to ask questions and if you can't answer them, look them up together. Find things they are interested in - and help them to explore them

First off - the VAST majority of kids who go to university, even the very top ones, attended state schools, so don't worry about not being able to afford private schools.

All you really need to do is support your dc, take an interest in what they're doing at school, make sure they do their homework, and just generally be a household that values education and considers it important.

All the other fluffy stuff, extra curricular, museum trips, foreign cultural holidays etc are nice to haves, but not deal breakers.

Trust me I work with deprived kids and children in need and the key thing is interested parents!! Read with them, check out free events at your local library, go to museums, and science museums, take them to education stuff and get involved!
It
Doesn't matter that you don't have degrees the fact that you care and want to help will give them a great advantage.
Encourage them to dream big and look into
Education careers so you can answer any questions they have