check this video for setup
http://youtu.be/hLox0ia8HDU
you get matches and a bottle of whiskey
and then... you combine the matches and the drink to make a fire.
but I don't know how to do that...?
Do you want it to be able to be combined anywhere, or just during one specific event?
There are several alchemy scripts that will allow you to combine items to create other items.
If it's for one event, you can use conditional branches in that event to check if the player has each item necessary. If both conditions are met, remove each item and go forward with the event (lighting the drink on fire and distracting him).
It should look something like
Conditional branch: Matches in inventory
Conditional branch: alcohol in inventory
remove item: matches
remove item: alcohol
(whatever you want to put for the actual event, like dialog, an animation, ect.)
Else
(the player says something like "I still need alcohol!)
branch end
Else
(still need matches)
branch end