Because the card I made yesterday had 3D roses on them I decided to make a pizza box to put the card in. I have done this for several 3D cards before and they have gone over really well.
This is the box with the lid decorated using Very Vanilla and Timeless Texture DSP. The box itself is constructed of Basic Black cardstock
To make a box for an A2 card, start with a 7 3/4 by 12 piece of cardstock, and score 1" all around the cardstock, and then 5 1/2 and 6 1/2". Make the box as usual, and decorate as you wish.
Here the card is in the box. I usually tie a ribbon around the box to keep it closed.