Inside the lodge, The Doctor's hat can be seen on the back of the chair by the grandfather clock. Every time The Doctor enters/leaves the lodge the hat remains on the chair. Yet in all of the outdoor scenes (except inside the poacher's hut) The Doctor is wearing his hat.
When the Doctor and Sarah go back to where they hid the explosives, the wooden board the Doctor placed to close off the side of the hiding place has been moved and is now at an angle towards the front, thereby exposing the explosives to view.
The Doctor chides Sarah Jane for throwing the box with the gelignite, stating that "Sweating gelignite is highly unstable." Gelignite can "sweat" (i.e. leaching out nitroglycerin) but it is completely stable in the absence of a detonator.