Frodo waited with Gandalf in the cave. Gandalf had warned Frodo that the cave was protected by many spells, and while inside it, Frodo was invisible to Sauron's Eye. Outside the cave, the Eye was very likely to jump to Frodo immediately, given how the power of the ring was growing. Sam and Gollum were still with Frodo, and Gandalf had given them permission to wander about outside the cave as they liked, though he warned Sam to keep a strict watch on Gollum, lest he betray them. Gandalf himself stayed in the cave with Frodo much of the time, using whatever wizarding tricks he possessed to see a clear way to Mordor to destroy the ring.
There was one day, however, when another wizard came to visit Gandalf. Surprisingly, Gandalf permitted that Frodo spend some time outside, though he was warned not to stray far. Frodo wandered out behind Gollum and Sam. Being in the sunshine had never felt so good. Moments later his happiness was shattered when he saw Gollum playing with a deck of cards.
"No" he cried. "He'll see! Sauron will see!"
With that, he grabbed the cards out of Gollum's hands, and tore them into pieces. He ran into the cave, cards in hand, carrying them to Gandalf.
"Burn them! Burn them!" Frodo cried.
Gandalf pointed to a top-hat on the table, indicating that Frodo should deposit his card shreds into the hat. Gandalf then took out his wand and lit the cards on fire.