A package is a pre-defined set of preferences for building a character, including preferences for ability increases, skills, feats, domains, spell school, spells, animal companion, and familiar. Each package also specifies the class it is for, as well as the starting gold and equipment given to a player character when that package is chosen at character creation.
Packages are primarily shortcuts for the convenience of players who do not want to spend time making choices during character creation and level-up. During character creation, if a package is selected (and confirmed with the "OK" button), it will determine the skills, feats, etc. taken for level 1. Then during level-up, if continuing in the starting class, this package will determine the behavior of the "Recommended" button. (If advancing in a different class, or if the player had selected "Configure Packages" during character creation, then the default package for the class will determine the behavior of the "Recommended" button.) The determination of what to choose is based on a set of priorities, with the chosen feat, skill, etc., being the highest priority choice that the character qualifies for. This allows some flexibility in accounting for decisions that may have been made by players without the aid of a package (including choosing a second class).
One drawback of packages is that they are just a fixed system of priorities, so have limited ability to intelligently adapt to unexpected circumstances. For example, if a character has weapon focus in the bastard sword and a package calls for weapon focus in the longsword, the second weapon focus will be chosen even though it is probably not really desired for that character. Packages work best if they are used consistently, with no customizations by the player. (Whether or not packages are useful even at their best is a subject of debate, though.)
Custom content[]
A package can be used to control the leveling of a non-player character (NPC) through the LevelUpHenchman() command, but usually only if that character started at level 1. For special NPCs, it may be desirable to define a custom package, as BioWare did for the henchmen in the Hordes of the Underdark campaign.
Packages are defined in packages.2da, with some associated information (such as feat lists) in the PackFT*.2da, PackSK*.2da, PackSP*.2da, and PackEQ*.2da files.