UT 2004 Patch (Final Version – v3369)
This should be obvious, but if not, downloading the latest and final patch will fix a wide variety of issues that were present in previous and release versions of the game. Make sure you pick this up first.
Windows 64 bit with AMD CPU Patch
Improvements on the final version patch for players to get a bit more optimization out of the game. Note the title is serious business, only Windows 64 bit, and only for AMD x64 CPUs.
X-Fi SoundBlaster Patch
Although this sounds like a patch for Sound Blaster X-Fi users, its actually a content patch created by Creative (makers of Sound Blaster cards) for UT 2004 to upgrade the quality of all the audio in the game. Back in the day this would be recommended for higher performance cards, however with the years that have passed, it will probably work well with noticeable improvements on most setups.
Mega Bonus Pack
This official content pack grants all the additions from the Community Bonus Packs along with the Editor’s Choice Edition of UT2004, granting the addition of new vehicles and a whole lot of maps. No reason to not have this.