Gmail: This is a tough one. Gmail has great spam filtering and a good interface. I've run my own mail servers in the past for work (qmail, dovecot, sieve, etc) so the backend wasn't a challenge - just spun up a Linode. I experimented with numerous different front-ends, squirrelmail, roundcube, etc until I found a really good one: rainloop. It took some tuning to get it to talk imap, but I've been really pleased with it.
Drive: This one was tough - there are a lot of commercial file storage systems out there, but largely I used Drive to keep live backups. I'm now using Syncthing, with one of the folders shared via s3fs - so I could drop something in the s3fs folder on any of my devices and it'd be available on the web in an s3 bucket in minutes when I need to share to other people. Cool!
Android/Google-Fi: Google Fi is just too good, I haven't found a good alternative to this. I'm going to need a new phone soon, and have been researching other alternatives. I'm not sure, with Google Fi, I'll be able to use any other alternative OSes on Android-style hardware, and I refuse to go the Apple route. Blech.
Google Docs: I've reverted back to using desktop apps (Libre Office) for spreadsheet and more complicated word processing, and installed Codiad on my dev server for day-to-day note taking and development. There really aren't any good FOSS, online, self-hostable office style apps. At least not that I've found.
Chrome: I've been mainly using Firefox, Brave, and Tor for awhile. Chrome/Chromium's network password storage was nice; but I've trained myself to use KeePassX/XC full time. It's cross-platform, and synced with Syncthing I'm never without the freshest copy. KeePassXC will even do TOTP, though keeping your one time password generator right alongside your password is a questionable thing to do.
Google Reader: This one hurt the most. I had a massive list with many custom filters. I replaced it with
tt-rss. Miniflux. The tt-rss guy is a jackass so I abandoned it.
DuckDuckGo. Startpage. I will bounce over to Google now and then when DDG's results are a little lacking, which they sometimes are - especially for looking for specific things to buy online.
Photos: I've always used flickr. There have been some design changes that people haven't liked about flickr's website, but I think they've only improved it over time. I'm happy to pay for that unlimited storage and instant backups for any pictures I take. I've been mulling creating a syncthing-folder automatic gallery app for awhile, but flickr works well enough. If flickr ever shows signs of being in trouble, I'll push forward with the idea.
Hangouts: Another service of theirs I really, really came to depend on and was furious when they pulled. You can still access it as a Google Fi user, but it acts pretty brain damaged these days. Most people I chat online have moved onto other services, like Telegram, Signal, or Facebook Messenger, or back to IRC. I detest facebook, but at least you can sideload 'lite' versions on android and sandbox facebook in a tab in Firefox.