Hello fightgainstalz and welcome to Talking Point.
Remembering things from years ago, but not remembering what you ate for breakfast is classic dementia - the oldest memories are the ones that remain longest.
Think of your memory like a bookcase - the oldest memories are stacked at the bottom and the newest ones are at the top. If you shake the bookcase the books that fall out first are the ones at the top. Every time you add another memory it will go in at the top and be shaken out quickly.
When your grandad thinks of you he is probably remembering you as a small child (the oldest memories last longest) and that is why he doesnt always recognise you. When you go to see him say, as soon as you see him, hi grandad its me "
your name" and he will be more likely to remember. Dont get upset if he still doesnt though, he will probably remember that you are important to him even if he cant quite place you.
As to not remembering how to shave, or how to store food properly - Im afraid that if he has forgotten how to do this you cant re-teach him (they will become new memories that will be quickly lost again) all you can do is take him step by step through how to do things, or do them for him. You will probably need to raid the fridge and throw out old food. Dont let him see you do it though and dont leave the old food in the house. People often get angry and have been known to take mouldy food out of the bin as "its perfectly OK"!!
If hes not eating, then little and often might be the way. Often people with dementia lose the feeling of being hungry and too much can overwhelm them. Try small portions on a big plate so that it doesnt seem so much. Is he having problems using a knife and fork now? Finger foods might help. Mum will sometimes say that she is not hungry, but if you put a bowl of cheese cubes grapes and little savoury biscuits next to her while you are chatting she will dip in and before you know it the food is gone.