Does it matter how big the warm brick or water bottle is when putting by your feet?

It does matter. For both warm bricks and water bottles, a larger surface area and higher water content allow for more heat to be transferred to your feet. This is because heat transfer is proportional to the surface area and the temperature difference. A larger warm object will have a greater surface area in contact with your feet, allowing for more heat to be transferred. Additionally, the higher water content of a water bottle means that it has more thermal energy (heat) stored within it, which can be transferred to your feet over a longer period of time.