Powering multiple circuit boards from one wall wart
You can use one supply and parallel all the connections providing:


All input voltages are the same.  
The supply can deliver more than the sum of all items current requirement.  


Since you say 9V is suitable for all items, then 1 is covered. For 2, check the maximum current rating for each and add them together. Then pick a supply that has a current rating which is equal or greater than this value (having some leeway is always a good thing, so multiplying by say, 1.2 is a good idea. Although it's unlikely all items will be drawing max current simultaneously, it's better safe than sorry - many cheap wall warts won't actually manage the maximum rating printed on them safely)

For example, if you have 5 items, all 9V, and current ratings of 50mA, 100mA, 150mA, 200mA and 300mA, then pick a 9V supply capable of at least 800mA. Multiplying by e.g. 1.2 gives you 0.8A * 1.2 = 0.96A, so call it 1A (or more)