In Antarctica there are no toilet visits possible on land (Antarctic Treaty/ IAATO regulations). If someone knows he/she has a frequent need for a toilet then this person has to take a bottle (e.g. a Nalgene bottle with a wide opening, sold in outdoor shops) with him/her.
One important tip is not to drink too much before the walk. Then during the walk only drink when feeling thirsty. For solid human waste we provide biodegradable poo bags, which have to be taken back to the ship for disposal.