Muddy Water Method - Place basin with muddy water on the ground between you and the tree. Step back from the basin a distance equal to that from your eyes to the ground.You should now see the top of the tree reflected in the water. If not, move basin and yourself. Distance from basin to foot of tree is the tree's height.

Tree Felling Method - Hold a stick upright in your outstretched hand. Sight to the tree you want to measure with the tip of the stick covering its top, and your thumb marking its foot. Then move the stick 90 degrees. Notice the point where the tip of the stick hits the ground. Stride the distance from this point to the foot of the tree to get its height.
When you want to measure the width of a river there are a couple of simple methods you can use If the river is narrow, try the Napoleon Method. If it is wide, use Step-Measuring.

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Napoleon Method - Stand firmly on one shore. Bend your head with your chin against your chest. Place your hand on your forehead so that the front edge of your palm seems to touch the opposite shore. Make a half-right turn, transferring the distance to your shore. The distance to the point that your palm edgenow seems to touch is the width of the river. Step it off.

Step-Measuring - Notice a rock on the other side of the river (A). Place a stick on this side, exactly opposite the rock (B). Walk along the shore at right angles to AB. Take any number of steps, say one hundred. Place another stick here (C). Continue walking for half as many steps as before. Place another stick here (D). At this point, turn away from the river walking at right angles to DB. When you sight stick C and mark A in a straight line, stop. This point is E. DE is then half the distance across the river. Step it off. Double it to get the full distance.