Less than people expect. Passports, a short written history of travel and prior applications, family details, and any earlier immigration decisions are usually enough for an initial comparison. Certified translations and evidence packages come later, once USCIS issues instructions for Form I-140G supporting documents through the official portal. Ordering everything in advance risks paying for documents nobody asks for.
Turn memory into a written summary
A one-page chronology beats a folder of loose papers at this stage. List each period abroad, each application made anywhere, and each change of status or refusal, with dates as accurate as memory allows. Mark the entries you cannot yet prove.
This summary lets a reviewer see the shape of the case quickly and identify which two or three documents would actually change the analysis, keeping early costs limited to what the assessment genuinely needs. Keep the chronology honest about its own uncertainty, since a confident summary that later turns out to be wrong is worse than an admittedly approximate one. Mark each entry as documented, recalled, or unknown, and note where a record could be obtained if it mattered.
A reviewer reading that page can usually say within minutes which two or three items would change the analysis, and the household then spends money on those alone. Ordering a full evidence package before anyone has identified what is decisive is the most common early waste in this route.