Did something similar, but 4 people (one was almost 6' tall) and no pets for 8 hours and the rooftop carrier filled. Ugh...the tortoise said:3 People
1 Dog
2 Skis (in roof box)
1 Snowboard (again in roof box)
Clothes, ski/snowboard equipment, food and booze for 4 days.
Travelled like this for 6.5 hrs. The car was PACKED.