There is a bug with putting items in a container in your inventory (the weight is not updated right away), which will let you bring as much as you want to the wastelands. Save first, since there is a potential problem exploiting this which can destroy items. See weight bug and disappearing chests

The trip to the wastelands is one way, so bring everything you may want later (dump any spare keys you are hanging onto, and sell all your loot if you want to buy charms and spell books).