Plebes don't "rate" being able to sleep on top of their blankets (yes, that's a privilege!) until after Plebe Summer, at the earliest. Like many things, the date when it's allowed will vary by company. Your Plebe will know when he/she can have a sleeping sack or spare blanket.
Cookies (especially home-baked) almost certainly will not be eaten by your Plebe during Plebe Summer. The cadre try to make sure that the Plebes don't fill up on junk food, so many food items (i.e. cookies, chips) get confiscated. After Plebe Summer, the Plebes will open packages in the privacy of their rooms. However, still try to send mostly "healthy" snacks. Many a Mid has trouble gaining weight during Ac year. That can make passing their physical assessments (PRTs) more difficult, and if they have to take uniforms to the tailors, it can be quite pricey!
Care packages are good, but my Mid has said that cards and letters have been more important than anything else. She said recently that she has kept every single card/letter sent to her this year. Photos of family, friends, pets (or garden pics!) are all good things to send. At various times this year, we have also sent jokes and trivia items, which have, in some cases, earned my Mid brief periods of "carry on!"
He should be able to meet his coach the day before I-day to drop off any athletic equipment. The best thing is to have him/her contact the coach of their sport, to work something out. Unless you have pre-arranged his/her sponsor family, your Mid won't meet their sponsors until well into Plebe Summer. I believe last year the "meet and greet" happened the week before PPW.