30amp 2 breaker sub panel
You can use the 2-space panel as it is.  Just split the hot so it connects to both lugs. However you must use a 2-pole breaker, or handle-tie all the breakers so they throw together.  Why?  You need a disconnect switch, and that's it!  And it must be 1 throw action.  

One of our crusades around here is to convince people that you are better off with a LARGE service panel, in terms of the number of spaces.  That is to say, 2-space panel considered bad; 18-space panel considered good.  Why? Physical expansion room.  The likeliest thing that will happen to you is that you will run out of breaker spaces.  This is an expensive and awkward problem, and it is easily avoided by getting an excessively large panel (for right now). 

Saving money is awesome. We'll help you do that here.  But the message for now is, a baby panel is the worst possible place you could try to save money! There's very little money to be saved (I joke about "a few latté's" but it's true), and so much frustration and cost when you hit the wall later. 

So take back the 2-space and get at least a 12-space.  

I'll even say to get a panel with a "main breaker".  That becomes your mandatory disconnect switch. The cheapest way to get a 30A disconnect switch is to get a panel with a main breaker >= 30A. (Since you're only using it as a disconnect switch, size does not matter). 

In the future if  you make your supply wire bigger, it just hooks up to the main-breaker panel. No need for an upgrade! 

Hooking up to the disconnect switch

If you got a main-breaker panel, you take your 30A 120V "Hot" wire and split it.  That is, you put two 6" pigtails on the 2 hot inputs of the main breaker, and wire-nut that to your 30A input (you'll need a big blue or tan wire nut).   Now you can fit breakers normally. 

NO MWBCs (shared neutral) circuits!  (if you don't know what that is, don't worry about it).

If you got a main-lug (no main breaker) panel, then you'll have to backfeed it.  (i.e. bring power "in" the normal "out" of a breaker).  Backfeed breakers require bolt-down kits, and bolt-down kits require 2-pole breakers.  So split the power to feed both "hots" of the 2-pole breaker.  This can't be a $80 GFCI breaker, you can't backfeed a GFCI! 

In a pinch, you could use something like a quadplex breaker. Bolt down the quadplex.  Then backfeed with the two inner (say: 30A) breakers and serve your loads with the two outer (say: 20A) breakers.  

There is also a "Tie the buses together" cheat that can be done, where  you run a wire connecting the two main lugs.  However, this doesn't buy you anything in a 30A panel.  Having too few spaces is still a huge problem.