While I don't believe clothing can be purchased at an outside store and sent in to an inmate (not enough profit for the prison, and too much opportunity to sneak in drugs or other contraband in seams or pockets, or even to soak the fabric in a liquid form of the drug and then to have it gotten out once inside the prison), the prison WILL provide basic clothing for an inmate.
The things your son wants are ALL things that are used as cash by inmates, used to trade for drugs and used to gamble with and to buy other contraband items with. It is past time for you to figure out EXACTLY what the prison will and will not provide, and how much your son is lying to you and manipulating you. Based on his past record, and his constant begging for money rather than efforts to rebuild his relationship and to earn your trust back, I would say he has not overcome his drug problems or his other problems while in prison. I would say that he is continuing to use you and you are enabling him.
In other words, at this time you are part of his problem, not part of his solution. I know that you feel guilty saying no to him. I know it is hard. Please, PLEASE, go to some Alanon or Narcanon meetings. If you cannot go for yourself, go for your husband and your son. Go for your relationships with them. It will help you establish and understand healthy boundaries, and deal with the guilt.
I also recommend reading the book Boundaries, by Cloud and Townsend. There is also a workbook that you can do with the book. It is amazing, and it really can be helpful.
One clue that you are doing the wrong thing is that you don't feel comfortable telling others what you are doing. That you feel bad telling your husband what you are doing is a major sign that you are doing the wrong thing. One way to think about what you are sending your son is this - how would you feel if your son overdosed on drugs in prison? How would you feel if you knew that he bought the drugs that he overdosed on with money that you sent him? Jeans, shoes, coffee, food, hygiene products are all used as currency in prisons. If he is still using, and you help him, you are contributing to his problems.
I know you want him to feel loved, but you can do that with a card and with emotional support. Physical things are NOT the best way to show emotional love. I am sorry that your son makes you feel that you must send him so much money if you love him, but he is WAY out of line to push you like this. He can get a job, even in prison, and WORK for what he wants and needs, like people everywhere else in the world do. Making his mother send him money is NOT the right thing for him to do, and he should be ashamed of himself. Where was he when you needed help with anything before he went to prison? What has he done to show his love for you? Why is this love a mom to him one way street and not ever a him to mom street? Where is his support and love for you? What has he done but push you to lie and go against your husband, the man who is there to help and support you?
These are just thoughts, and I certainly am NOT judging you in ANY way. We all have done things we may not be proud of, I know I have at times. I have made WAY more than my share of mistakes over the years, so I am not in any way throwing stones or judging you. I just think that you should ask the prison what they provide and then tell your son to figure out how to survive on what they provide and whatever jobs he can find at the prison. Because they will let those who want a job and who will behave themselves get a job. And maybe going without would be what he needed to motivate him to behave long enough so that he could get a job.
Big Hugs, Your Stillwater Friend