Which pioneers/explorers are you asking about?
Where were they exploring? When were they exploring? What technology was available to them? Were they exploring on land or by sea? Or in space?
Where you're going affects what will and won't be useful to you.
Don's answer, however, is good for pretty much anywhere--by land or by sea, a good, sturdy knife (and the means to keep it sharp) is always going to be useful. Rope--lots of it--is almost as handy. Fish hooks won't be much use in the desert, though. I'd add a sewing kit--needles, thread, spare buttons, etc, because when you're in the middle of nowhere, you can't get yourself a new pair of pants--you have to fix the ones you have.