At minimum, I would get a surge supperssor, such as the Progressive Industries Smart Surge. Depending on whether you need the 30 or 50 amp version, these are often under $100.
In addition to surge suppression from lightning and transients, they typically tell you if you have a reverse polarity condition (ground and hot wires swapped).
You can also get an advanced model that are both a surge suppressor and also monitor the voltage and shut down the connection if the voltage is too low (brown out condition). Examples are the Surge Guard TRC30 and TRC 50. These are much more expensive though, and are well over $200 for the 50Amp model.
You may also wish to consider a voltmeter to monitor your coach, such as the Prime Products AC Power Line Monitor, especially if you purchase the less expensive surge suppressors. These are only around $30 and for the cost, I'd buy one and plug it into an AC outlet and leave it there.
Speaking of power, you will also certainly want a 30 to 50 amp "dogbone", which allows you to plug a 30A coach into a 50A outlet, or the reverse (depending on the version you buy). These are a bit dangerous though - especially the 50A to 30A converter, as you can overload the power pedestal. So, when using these you have to to monitor the load to make sure you don't exceed the current limits.
If you have 30A power, you can also buy a 20 to 30 Amp dogbone with the same caveat (I might not use one of these with 50 Amp power though).
If you have 30A power, buy a 50A to 30A dogbone adapter (plug a 30A cable into a 50A shorepower pedestal), and a 30A to 20A adapter (plug the 30A cable into a 20A pedestal). The 30A to 20A adapter also allows you to plug into your garage power if your RV is at home.
If you have 50A power, buy a 30A to 50A dogbone adapter (plug a 50A cable into a 30A shorepower pedestal).
Again, when using one of these dogbone adapters, if you are decreasing the power capability - such as plugging a 30A power cable into a 20A power source, you should not run the Air Conditioner or any other high power appliance. You should be able to charge your batteries and run a few low-energy devices though.
For example, we often plug our 30A coach into our garage 20A receptacle for running the refrigerator (or more accurately, not running the coach battery down) the day prior to leaving. That way, we can transfer our food just prior to leaving to the cold fridge, and it will keep for 4 hours or so.
If you are plugging your 30A coach into a 50A source with a dogbone, well then there are no restrictions on limiting your power.
The reason you need these adapters is you might end up at a campsite only having a 30A or 50A (or in some cases 20A) service. Again, heed the restrictions on limiting the current as needed when using a dogbone.
Also,, consider a 25ft or 50ft shorepower extension. The one you got with the coach is probably a bit on the short side. I needed to use my 50ft extension on three occasions last year, as my coach cable is around 40ft and was not long enough for some campsites.
The only thing that works on a RV is the owner...