As the cold front has hit and passed already, all preventative measures are useless, that horse has bolted, figuratively speaking.
Your next step is to assess the damage and work from there. After a frost wave, some plants will look dead (and some will be, frankly), but can recover by regrowing either from the roots or the stem, depending a bit on the plant. Others may look mostly fine, but cellular damage will become obvious later. Unless you plan to redo your landscaping anyway and take this event as a catalyst, I would recommend to wait a bit longer and watch what’s going on over the next few weeks. Remove obviously dead material, from leaves to whole plants as needed. Remember that there are other natural causes that can seemingly destroy vegetation and it bounces back afterwards - think wildfire or animals.
When you see new growth, consider fertilizing. I won’t give you a “one fits all wonder mixture”, as different plants have different requirements and you need to take that into consideration. You can either use a store-bought product or get some compost or well-ripened manure (You hopefully do have a compost heap? That’s where the banana peels and tea leaves should go, not directly on your plants.).
There is no immediate need to fertilize now if your plants were growing well before - you are looking at “smaller” plants with less foliage and a just restarting growing season. That means your plants will process fewer nutrients. At best, an excess would just be washed away, but too much may also lead to very undesirable effects like “burned” roots or too fast growth which may look pretty sooner (if the plants don’t get just lanky), but can also encourage pests like aphids to make themselves at home in the overly soft greenery. When it comes to fertilizing, rather err on the side of less if you are unsure.
If you have to plan for recurring frost events or are dealing with usually dry conditions, mulch can be your first line of defense. It keeps the soil moist and shaded in the summer and protected in the winter.