1. I need to withdraw the cost of a semester meal plan from my son's 529 before 12/31, right?
Yes. A 529 withdrawal is taxable income *initially* in the tax year it is withdrawn. It's taxability is offset by the qualified and allowed expenses it is used to pay for *in the same tax year it is withdrawn*.
2. ditto for 1/4 of the house utilities during the semester (gas, electricity, wifi, garbage, water) since my son shares the house with 3 other roommates.
Yes. The same "timing rule" applies as explained above
3. Do I have some time to figure out whether I am going to charge my son rent? He has never filed a tax return before. He earned about 3K over the summer.
Are you asking about this for the 2020 tax year? At this point if you're considering charging him rent for 2019 it's only doable if the student is already the named beneficiary on the 529. At this point, it's a bit to late (I think) to change the beneficiary if it's not the student already. If you've already made any withdrawals and then you change the beneficiary, the first named beneficiary will receive a 1099-Q for the withdrawals made prior to the change, and the new beneficiary will be receive a 1099-Q for any withdrawals made after the change.
