Things I learned taking my kids when they were young:
- attention span of a fruit fly, seems about right :-)
- bring snacks
- bring books and read to him
- when it's cold, don't go
- when it's "buggy" don't go
- keep in mind his legs are VERY much shorter than yours, going over things will be hard (trees, rocks, branches, streams).
- his legs are also short for walking distances, he will get tired faster than you.