My wife has just entered the third trimester. Would you have any suggestions for her overall well-being? Also, what would be an ideal midnight snack?

What I would suggest is to be sensitive and reassuring. She may start worrying more about the weight gain and become more conscious of her growing bump. Continue to shower her with hugs and kisses and constantly let her know that you still find her beautiful (or even more beautiful now). Go for walks with her as it could help ease some physical discomfort such as back aches. Midnight snack I would recommend hard boiled egg, veggie sticks (like carrots) or apple/pear slices with cottage cheese, or a bowl of cereal with milk. :)