The following suggestions are all assuming that the plants you are using are not from along side a road and contaminated by vehicle exhaust or they were not sprayed with any weed killer or any chemicals at all. All the washing in the world won't get that poison off of the plants.
One major source of infections that can become a problem post SHTF are bug bites. Right now, they are just a pain in the butt and a irritation, but when you start to scratch a bug bite with dirty finger nails, then things change. We already know, that keeping clean is going to be hard after the SHTF, but I wonder how many have thought about just what that truly means? Just a scratch from dirty finger nails or a scratch on a dirty arm can lead to potentially life threatening infections. The best defense against bug bites, like mosquitoes or gnats will be prevention. Bees, wasps and hornets are a different matter I'll address later. To keep mosquitoes away, I've found a mixture of pennyroyal, peppermint and lavender to be very helpful. Do not, I repeat, do not use pennyroyal any where near a pregnant woman as it will cause miscarriage. You can grow the herbs yourself and make either real strong teas or tinctures. Mix them in equal parts in a spray bottle and spray yourself frequently as the mixture will sweat off easily. This mixture can be played around with to find the right mix for you and if you have any pure vanilla extract you feel you can spare, you can add that to the mixture also. The dried herbs can be spread around any area you want to keep bugs out of. But I can't emphasize enough the importance of keeping pennyroyal away from pregnant women. Any herbal remedy should be used with caution with pregnant women and the only one I feel comfortable suggesting she use would be peppermint for morning sickness. There is an herb you can grow around your home called Bee Balm that is reported to keep bees away from your house and the leaves made into a tea will help soothe a bee sting. Me, I am deathly allergic to bees, wasps and hornets so I try my best to just not be where they are. Post-SHTF, I am going to have to be doubly careful, since there won't be any Epi-Pens available and I don't know of any herbal remedy for anaphylactic shock.
You'll need to make a poultice if the cut or burn is bad enough and all you'll need for that is a piece of clean cloth and what is growing right outside your backdoor; good old Plantain. The usual method of making the poultice was to chew the leaves, put them on the injury and tie the clean cloth around it. Sad to say, but when TSHTF, many mouths may not be as germ free as they should be, so just place the washed leaves in between two pieces of clean cloth and grind them with a rock, you don't have to totally destroy them, just grind them up enough so the juice is released. Tie this over the wound and change it out every day. In some cases, you'll be surprised at how fast the wound will heal.