For 9-years I used home-made wooden pieces of different thicknesses to which I would build platforms of required height to pull the trailer wheels onto. I had plastic levels attached to the front and side of the trailer which yellowed over time.
With the purchase of my new travel trailer I purchased a new leveling system to which both the wife and I find a lot better.
I use a Hoppy Hitch Level
which permanently mounts to trailer tongue for both side-to-side and front-to-back leveling. Comes with a cover as well. I back in or pull into the RV spot. The wife takes a look at the level and turns the dial until it becomes level and a pointer indicates number of inches required for adjustment on the appropriate side. We than add the required number of leveling blocks
from the convenient storage bag. We purchased our leveling blocks at Wal-Mart which we found to be the least expensive at that time. Could possibly be the Lynx brand but I can not remember. (I have two bags of these and use some under my tongue jack and under my stabilizer jacks when required)