To get even more enjoyment from your favourite track many people decide to fix it to a board and decorate it with buildings, obstacles, garages, track side advertising, and landscaping. Above are links to there respective topics, with descriptions evaluation of different methods of scenery construction:

My advise is read all the methods used and decide for yourself which one fits your circumstances best. As what may have been right for me might not be right for you

Scenery can be bought or built, expensive of cheep. It all depends on your skill, the amount of spare time you have, and your budget. Ready made buildings and structures are great for when you don't have the time or skill to create you own. They are expensive however especially if you buy good looking models, (the ones without the plastic look to them).

In the case of vegetation you can buy trees, but you will still have to do all the grass an hill work, as ready made alternatives just don't exist. Landscaping is the easiest and most fun stuff to do. If you are building track for you kids, this is often the part of the project which you and them can work together on. Working with papier-mâché and model-rock is great.

I would like to repeat my self, read all the methods used and decide for yourself which one fits your circumstances best. If you haven't got the money, build it. If you haven't got the time, buy it.