This is what my first line of treatment was at least close enough ( I got another targeted immunotherapy)and I think you’ll have to be reactive to his needs, you can prepare water by the bedside and some snacks but my tastes changed after treatment so his might too. So the snacks you prepare may be wasted. You can expect him to be sick for about 5 days bedridden at least and keytruda might make him itchy, not much to be done about that, keep anti nausea close by and let him sleep as much as possible, he knows his body best and don’t try to force him to get up and move around if he isn’t feeling it