Why is the moment with the berries an act of rebellion against the capitol?

Katniss and Gale are supposed to be preparing for the lottery..... instead, they are enjoying each other's company as if it were a holiday and making fun of the process. In this, the pair is rebelling against the capitol by eating bread and berries in the woods, a place that it forbidden to them.

This section is located in Chapter One. My etext does not have page numbers.

"Suddenly he falls into a Capitol accent as he mimics Effie Trinket, the maniacally upbeat woman who arrives once a year to read out the names at the leaping. I almost forgot! Happy Hunger Games!"

"The day is glorious, with a blue sky and soft breeze. The foods wonderful, with the cheese seeping into the warm bread and the berries bursting in our mouths. Everything would be perfect if this really was a holiday, if all the day off meant was roaming the mountains with Gale, hunting for tonights supper. But instead we have to be standing in the square at two oclock waiting for the names to be called out."