The school books were definite. As were the weapons. Guns and knives mainly, but Ranma had made some simple bombs too. She would have gone with blocks of C4, but the detonators wouldn't work in Hogwart's halls. Plastic spheres filled with gunpowder and a fuse would still work, as there was no electricity required. The blast might not be quite as large, but given that the reactions of your average wizard having something tossed at him would be to catch it and inspect it closely, it would be large enough.
Idiot wizards. If someone tossed anything with a fuse at you, common sense would be to throw it away, preferably out a window, as fast as you could. Or at least to put out the fuse.
Herb still abstained from carrying weapons around as, from a certain view, she actually was a living weapon. Instead, she used the space to carry more books and arcane equipment, along with a large amount of candy.
It was fun to watch kids jump through hoops for a chocolate frog. And every so often, they would find something useful. Combine that with the fact that rather than realizing they were just toying with them for their own amusement, the bribed kids had cemented positive images of them in their heads and were more than happy to 'run errands', it was well worth the cost of a little candy.
Zombie-James had flat out insisted that Harry carry a sack of 'pranking supplies' with him. He also suggested that they look into finding a special map that he'd made in his school days. Zombie-Lily applied a frying pan to his skull when he suggested they 'target Snivellus, for old times sake'. He spent the next hour looking for it, as it had gone out the open window.
Honor among Thieves, Chapter 10