The title says it all really but I'll go into detail a little more.
One of the handiest tricks I ever discovered earlier last year, was to get a second debit card issued specifically just for subscriptions.
Not so long ago, I used to just have my primary account tied to my debit card, and a couple of others that weren't accessible through any physical means.
A few times, I would get a bit too eager to try out subscription services and slowly, my primary account would get eaten. Similarly, surprise yearly renewals would suddenly eat a portion of my bank account to my horror.
My "fix" for this was to transfer all of my money instantly out of my primary account and across to another savings account. I'd keep a minimal amount on my card and perform transfers on the fly as I needed.
This actually caused me a lot of grief once when I was trying to check into a hotel while visiting America. My bank actually had maintenance on their mobile app so I was stuck with just shy of the required bank deposit and no way to access any of my money. Thankfully, the clerk let me pay it in the morning.
It got particularly bad when I joined a gym. They would do their debit charges on a Friday but I swear it never felt consistent. Sometimes it would be on a Saturday or it would be first thing Friday morning. More than a few times, I forgot or be late, causing both the charge to decline and myself to pay a dishonour fee as I didn't have enough.
Now, at this point, you may think that I should have been more vigilant in transfering across the required amount which brings us full circle. Sometimes I would perform a transfer for the required amount the night before... only for a subscription renewal to eat into the balance, causing a decline because what the heck, suddenly I don't have enough.
Anyway, it occured to me that when you break it down, there are two streams of charges: those that are controlled (ie I physically swipe my card) and those that I would call erratic. The latter are often a known quantity but soetimes they're a moving target, sometimes my dumb human brain forgets.
For the most part, the feeling is that of being inside of an interrogation room. That is to say, there's a kind of one way mirror where I don't really know what could jump out at any minute and eat my wallet.
So anyway, what I did was requested a second debit card that I use entirely just for subscriptions and the like. I don't do anything fancy, just roughly eyeball how much is expected to go out based on last month and transfer it in. Every week or so I'll move amounts in and out based on how close to the mark I've been.
A very handy side effect is that you've also got a clear view into your recurring expenses. Often times you can forget you're subscribed to something for a long time because the transactions are buried amongst your life stuff.
With your subscription only bank account, you've got a continuous feed of things you're subscribed to and hey, you didn't even need to pay a SaaS company to figure it out!