1.

They are sorry they missed the end-of-term party.

wish

They    the end-of-term party.

2.

I'm very bad at spelling, which is a disadvantage.

better

If    at spelling.

3.

I don't like you arriving late for class.

would

I    late for class.

4.

I regret not studying Russian when I had the chance.

wish

I    Russian when I had the chance.

5.

I'd like to be brainy, good-looking and rich!!

only

If    brainy, good-looking and rich!!

6.

Unfortunately our teacher never takes us on trips to museums.

wish

I    us on trips to museums.

7.

She regrets sending her son to a boarding school when he was 11.

wishes

She    her son to a boarding school
when he was 11.