Power cord should come with travel trailer. Most of the time, a cheapie sewer hose is included, but you will want to get an additional one for those times when you need it. Plan on buying a water hose and filter if you want to use a filter.
If you are going to buy a surge guard, you'll have to determine what you want. I use a Progressive Industries EMS system (30 amp portable for my trailer). For years, I didn't use one, but finally bought one when we bought the Minnie and I'm glad we have it as it has been useful several times.
A power tongue jack is also highly recommended. Some dealers include them and others don't. I wouldn't have a trailer without one, but it is a personal preference. Same goes for slide toppers.
You want to check carefully what packages of upgrades are available from the manufacturer, and review carefully the specs of any trailer at a dealer for what package(s) came with the trailer. A really stripped down trailer may not have a spare tire! And, some packages may be actually required by the manufacturer....which is kind of crazy because then it shouldn't even be listed as a package but just as standard equipment.
