Full Storage

You need to collect storage upgrade items. These items are the security cameras, padlocks and storage bars. You can find them by tapping on the citizens thought bubbles or if youre brave you can try your luck finding them at the Global Trade HQ. I wouldnt use simcash to buy them but it is an option.

CJ

You can also sell some of the things you have in storage on the Market to make room for more important items