Also there is always the option of holding just one 0.25³m³ Block in your Hands directly after picking it up. In general you need an empty Hand to pick up things from the World, since they turn into Blocks once they stop moving, you dont just magically suck shit up, like in Minecraft.
And there is ofcourse always the ability to build Microblock alike Structures that are like 0.0625m thick, and use those Panels as placeable Walls. Kinda like a Bamboo Panel or so.
Not to mention, to build a Brick Wall you dont frikkin craft a Block of Bricks and place that down, you place individual Bricks and put Mortar on that. Though technically you CAN make a Panel out of Multiple Mortar-Connected-Bricks and place THAT down too. 
Note: Because there would be people who would really hate such Inventory Limitations, they can start up with a Bag of Holding alike Item to increase their Inventory Size if needed.