Some common categories:
(1) Financial: account statements (pdf, paper, etc), transaction CSV/ofx/etc, insurance policies, financial institution correspondence (confirmations, T&Cs, etc), tax forms, deeds/titles, loans, debts, contemporaneous records, paystubs, employment letters, receipts, etc
(2) Health: test results, diagnoses, medications used, doctor info/correspondence, vaccinations, hospital interactions, statements, bills, etc
(3) Product and services info: products purchased, maintenance info, warranties, replacement parts, recall notices, class action events, professional used (CPAs, lawyers, contractors, plumbers, etc), etc
(4) Personal legal and other documents: wills, trusts, health directives, pre-nups, legal settlements, personal contracts, rental agreements, government IDs, immigration/naturalization docs, law enforcement interactions, etc
(5) Memories and other info of sentimental or other value: pictures, videos, cards, recordings, music, diaries, clippings, personal notes, etc
For many of these one might ask the usual questions:
A. do I have a reason/obligation to retain it? for example, tax authorities often require certain classes of record keeping. sometimes commercial entities make false claims in retrospect that you can only rebut with evidence (even major banks!). some documents can end up only being used by heirs at end-of-life (ex: basis information for assets like a home, which can require proof of improvements over the years, depreciation claimed if the home was ever rented, etc)
B. is there a downside to retaining it? clutter, hard/costly to move, identity/other theft risk, physical decay over time (ex: obsolete storage formats (VHS, mini-DV, blueray)), etc
C. will I (or the appropriate person) be able to find it when I need it? physical paper vs electronic mgmt, indexing, filing, passwords, legacy services for transferring access.
D. can I actually retain it? backups, water damage, fire, theft, physical safe management, etc some online services don't provide any/easy export of data, many have inconsistent retention policies (ex utility companies)
Some of the categories above have specialized software and services dedicated to them (ex: photos services, quickbooks, etc) while some are more ad hoc (goog drive, dropbox, local HDD); even specialized services often fall short on key matters (quickbooks doesn't track statements afaik); many specialized systems have various platform limitations (no turbotax on linux, say); many vendors try to play various lock-in tricks; some vendors go out of business or discontinue products over the years; some institutions are very paper oriented so one perhaps scans or tries to limit paper delivery; some services place data in the cloud creating security exposure; etc etc