Bear in mind that there's a lot of utter bollocks on this thread.
They're not going to turn away a family with accommodation and return flights booked because they don't have 'enough' spending money with them.
Even when the passport control officer at Menorca airport asked me where I was staying and I said 'a camper van' which was true, he didn't bat an eyelid or question us any further.
They might start looking at the means of someone who turned up on a one way ticket and a vague plan to stay with a friend but otherwise, not an issue.
Debit or credit cards can be the cheapest way, or a very expensive way, but it absolutely depends on which card. Some are unbeatable in terms of exchange rate and lack of charges, but others will charge a fixed fee for every transaction, as well as take a chunk of the exchange rate, so work out very expensive if you use to pay for every last meal, coffee, ice cream etc.
For the last few years, I've found it very hard in Spain to find a cash machine that doesn't charge, so we now take a smallish amount of Euros (£50 to £100 worth) and also make sure we have plenty available in our Starling accounts and just pay for most things with those. We also have a Santander Zero credit card with a high limit which also doesn't charge any fees or loading and we use that if we need to leave a hire car or hotel deposit, so it doesn't impact our normal spending.
Have a lovely time OP.