This post contains affiliate links. I am not responsible for the outcome of using this advice, it is things that have worked for me, so use at your own risk.
This is a list of items I keep on hand at all times. Some aren't really first aid items, but health and grooming, but these are all things I believe guinea pig owners should have in their cupboards! Guinea pigs don't show they are ill until they are very sick, and having the first aid items at home can prevent a midnight run to the store -- and hopefully bring relief to your little one. This is NOT to replace going to the vet, many times you will need to go to the vet for antibiotics, but this is to help see you through until you can get to the vet -- or to supplement what the vet is doing.