If you are carrying your maximum allowed weight for items and want to carry some more, do the following:

1. Click on the item's on the screen which you want to carry.
2. Open your Spell Book and select any spell, most preferably one which doesn't need any ingredients at all, like "Ice Dart" or "Unseen Shield".
3. When you're at the page where you can add the ingredients for the spell, click on the "Room" icon in your HUD, the one located at the top-right. This will display all the items in the room which you clicked in Step 1.
4. Add the desired items (maximum five) to the recipe slots and mix the spell. The item's you put in the slots will be automatically added to your inventory. Keep in mind that now you're over encumbered to an unknown amount and you would have to repeat the process if you wanted to carry any more items, so it's better to find a good place to unload all your extra items and where you'll have easier access to them when you need them, like the corridors on the main studio.