ofbiz学习笔记--Which variables are available in screen context?
These are the most important (most used) variables. To have more details, check out ScreenRenderer.java populateBasicContext and populateContextForRequest methods.

This means that you don't have to worry about these variables : they are available from the 1st line of your scripts (BeanShell or Groovy)
parameters (of course)

delegator
dispatcher

security
locale
userLogin

webSiteId
autoUserLogin
person
partyGroup
timeZone

request
response
session
application

javaScriptEnabled

sessionAttributes
requestAttributes
requestParameters

eventMessageList
errorMessageList
nowTimestamp