RBF many times. Most recently was doing an in-person P2P exchange via Vexl.

No blocks were mined for 40 minutes, so I was constantly bumping the fee.

Yes. Electrum and Sparrow are very good for using these techniques. There are already some options for your "low fee stuck tx" in the mempool, to accelerate them, bumping the fee directly to the miner:

There's also another option named: Child Pay For Parent (CPFP) and RBF (Replace by Fee). Always set your wallet app option to use RBF, is the easiest way to push a stuck tx. CPFP is more expensive and with some other trade offs. One particular aspect of CPFP is that the RECEIVER COULD also increase the fee for a tx that is pending. You can do that in Electrum and Sparrow wallet.

Read more about CPFP here.

Yes, and likely to use it more often these days

Used RBF never CPFP

Yes: #145718

These are good exercises to do for yourself, to practice, and to de-mystify some of the nuts and bolts of how transactions work, esp in real life conditions with full mempools, etc.

Yes, have used RBF (via Sparrow) because it helps ensure your tx gets confirmed within a reasonable time when fees go up unexpectedly

I've used both. Basically in situations where a TX was sent and the mempool ballooned just after. Normally use RBF on my own TX, but I've used CPFP on a TX that I'm receiving. My preferred setup is Sparrow, which makes it all pretty easy.

Yes, both.

When there is fee spike in mempool and I need tx to confirm faster, for example, with P2P Bitcoin trades vs fiat.

I have used both. RBF is pretty straight forward. CPFP is a little trickier because you have to get two transactions through when you use it, so you need to do the math to make sure that you are paying enough sats / byte to get both into a block. For example:

I fat finger a transaction and submit with 1 sat/byte. I use CPFP to make a new transaction at 10 sats/byte, thinking that will suffice as mempool fees are around 8 sats/byte in this example. However, i did not do the math! Because i need to pay for two transactions ( thus twice the space in the next block ) my effective rate is ends up around 5 sats/byte leaving me still unable to get my transaction confirmed. I could then do another CPFP but now i have 3 transactions to pull through into the next block... so i better do the math right this time.

CPFP also comes from the change of your broadcasted transaction, meaning you cant do it for a utxo where you send all or almost all of the sats.