I think it's good to keep in mind that the thing that started the "tin craze" were the surplus "SAS survival tins". They were designed not to be survival kit, but to be something a soldier could carry easily to supplement the large amount of gear they already carry with the kind of survival gear they would rarely, if ever, use. Soldiers just don't do much living off the land.
IMO, this is exactly how they should be used: as a supplement of gear that you rarely, if ever, use, but could be of use if you get trapped out longer than you expected. For me, this would be signaling items and the typical snare kit.
Water purification is often missing in these kits, but let's look at the thing just as, if not more likely to kill you: shelter. A tine such as this does not, nor can it have, a serious shelter component. Even the cheap, nearly useless throw away space blankets would take up nearly the entire tin, and the good blankets are far too large.
In terms of water purification and shelter, these are things you should always have on you.
Your clothing should be your primary shelter, and there's no reason not to have your jacket or coat with you, even if you tie the arms around your waist, or rig it as a roll on your back. This plus a fire should carry you through a night.
For water, even in everyday life, it's rare for me to not see some sort of metal water bottle (usually 5L aluminum or stainless) sticking out of a purse, murse, day pack, carabinered to a stroller, etc. I've seen picture after picture of your guys and your "brew kits" (that strangely don't have any brews in them.....

) in your Maxpedition or other bottle carriers and paracord slings. There's really no excuse not to have them with you.
Taking those things with the knives most have on them, the lighter in the pockets, firesteel on the sheath or in the pocket, and your tin of tinder, maybe some trail snacks in your other pocket, and an unexpected night out should end with telling your friends "Yea, I pulled a dummy move, got turned around too late to get back. I thought I was going to be in an all-out survival situation -- I mean I only had one packet of coffee/tea bag left in my brew kit when the sun came up!"