I think waiting until a few weeks before they leave and then trying to teach them anything is leaving it too late. It's much easier to learn a skill by watching and helping over the years and gradual release of responsibility. I do, we do, you do. You start to take ownership and see this as "your job" rather than expecting someone else to do it.
Yes you can get recipes online or in books but it's not the same as learning in action from someone who knows what they're doing and can correct you along the way, assist, model. If you haven't touched an oven until you are 17 then you don't have the confidence to try things out. When you're a student, money is tight do you're not going to waste a lot of money and time on trying to do a big elaborate meal that might turn out shocking.
I think we don't really have a food culture in the UK as they go in other countries, where grandmother's recipes and skills will be passed on with pride, that connection to heritage.
I remember shortly before I left for uni my mum trying to show me how to roast a chicken and it just seemed baffling and too much, because I had never see. Her do it or helped before, I had zero existing skills. She later said she had tried to teach me but " I wasn't interested".
On the other hand I had been helping with cleaning, clothes and baking for years and am skilled and confident in those areas. I lived in beans and potatoes and ready meals at uni. Only now beginning to up my skills. In my case I think my mother just didn't really have many skills in this arena to pass on! It's fine; I love her! She worked full time and she did her best.
My MIL , on the other hand, is an excellent cook and was a SAHM. Sadly she didn't pass on any of these skills to my DH so he is having to start from scratch like me! He is also totally clueless in washing and cleaning, shrinks things etc. He has been taught the "male" things about cars and lawnmowers. I really want to try to involve our DC in all the jobs and pass on everything we know!