Hi I have reached level 20 and bought about 5 backpack SDU’s but cannot find them in my inventory to apply them. Could be I am looking in the wrong place. I check my backpack area under all the different categories. Is there somewhere else I have to look. Stuck on 12 items since the beginning.
All help appreciated.
Cheerio
Are you sure you bought SDUs for your backpack and not the bank? In either case, they are applied automatically so they aren’t useable items like in the first Borderlands.
When you buy the upgrades in TPS (and BL2 for that matter), they are automatically applied.
One note of caution: in Crazy Earl’s store, the backpack SDUs show up as a single item on the right of the display, while the bank SDUs are on the top-left above all the ammo ones. If you’ve been purchasing backpack upgrades and not seeing your backpack slots increase, it’s likely you were actually buying the bank ones instead.
Edit: Ninja’s!
If anything it’s kunoichi’d 
That sounds weird.
That is what I did. Dang! 
Mistakened the bank for the backpack SDU’s
Thanks!