Do you see the trend in the few responses you got?? This is normal kid behavior..you are not alone!! Time management, organizational skills and "remembering" come with maturity..and from caring. I know many adults that struggle with all this...and it comes from a lack of interest and not wanting to make a change...but also not knowing how to change. Sooo, it is great you are looking to help him now.
It will come with time...put painful to watch the process eh??
Some things I do that a friend/child behaviorist mentioned was to use situations at home to teach remembering. One of my son's teachers also mentioned this too. You ask questions...ask them to give you the answer instead of you giving an endless verbal 'to do list" that they ignore and say, "uh huh..I know..I will Mom!!"
Heres a morning scenario ,goes something like this "Good morning Joe Schmo...we have to be out of the door in 30 minutes to get you to school on time. What are YOU going to do to make that happen?" Then let him come up with 3 or 4 things he needs to do. If they stumble then maybe you give some hints like...shower first,get dressed and come out for breakfast and we can talk about the rest. Once at the table then ask what they need to do in the next 15 minutes to be out the door on time. It gets them thinking...puts the responsibility on them..and they say it out loud which gives ownership.
Ask questions instead of telling him what to do. "Hey Joe Schmo...I wrote this check for your lunch..where are you putting it in your backpack? When do you plan to turn it in to the lunch lady?" "Hey son. I see your dishes from breakfast still on the table. Are you done? Oh great...glad to see you enjoyed it. Where does the dirty dish go when you are done?" Wait for HIS answer and then walk away saying "Thanks!" He may stand there for a second...but he will probably walk and put it in the sink or dishwasher. I swear it works!!! We use this tactic on all 3 of our kids..it works!!
I can't stress enough how important it is to ask the question(pointed directly toward the end behavior you are wanting) and then allow them to give the answer. Kids tune out parents..tune out endless directions.
Don't fight with him about it. He is learning from making mistakes...learning from the 0's on his homework. He is earning his grades..not you. You can encourage and reward when you see he turned in an assignment. Everyday we see all our son's assignments turned in we talk about it. Sounds a bit redundant and childish for our 7th grader but they need the constant praise for small accomplishments. In the end all the small accomplishments will lead to big accomplishments.
Good luck and best wishes!!