To be very comfortable

It's freezing cold outside, but tonight we'll be as snug as a bug in a rug at home, in front of the fireplace with a warm afghan and a nice cup of hot coffee

Fuori fa un freddo cane, ma questa sera staremo da papa a casa, di fronte al caminetto acceso, con un bel plaid e una bella tazza di caffè bollente

The earliest example of this rhyming expression dates back to 1769 and is found in Stratford Jubilee (author unknown)