Don’t know how much help this is but you are using the shift function to save up some buttons, right?
In that case you can check the official website for ipac to see all keymappings
http://www.ultimarc.com/ipac2.html

But if you’re just trying to figure out how it all works and have a few buttons to spare I would recommend that you use specific buttons for at least the main functions like insert coin to get faster access to that in a stressful situation without having to think about which button combo or how to flip the stick etc to insert a coin or exit the emulator.

I’m using the iPac in my cabinet too (shameless plug below)
[img]http://i.imgur.com/DOR8A6P.jpg?1[/img]
and I simply used the 2B connection (lower right corner seen below) for a specific exit emulator button (ESC), so no need for the shift function there if you have an exit button, and I used the 1COIN connection (lower left) on another button for player 1 insert coin.
[img]http://i.imgur.com/eMwIhAw.jpg?1[/img]
I also used specific buttons for menu (TAB) and menu-select (ENTER) but that turned out to be quite useless atleast in my case since I’ve never really pressed those buttons after the initial setup was done, and if I really wanted to I could’ve used the shift function for that. But you learn as you go and I’m using the menu button for EmulationStation now so it’s not completely useless I guess.

Hmm, I see that there is a “Coin A” shortcut if you use the shift function with button 1, maybe that means that player 1 get a coin with player 1 button 1 and player 2 get a coin with player 2 button 1? But I don’t know really, sorry, I think someone else have to advice you on this.
There is some info that you can make your own shortcuts and macros on the IPAC website though, no idea exactly how but it seems like you can do pretty much anything with it if you invest some time in it.