Can anyone recommend a grocery store or market near the Vondelpark to purchase a picnic lunch? Thanks!
Google "Albert Heijn Amsterdam", you'll get a google map with locations. There are two near the park. Its a standard grocery store, nothing fancy. They take cash only
There are several supermarkets around Vondelpark. Albert Heijn accept cash and debit cards. Lidl and (most) Jumbo supermarkets also accept credit cards. Marqt is card only.
I really liked Marqt - I went there several times and thought they had a nice selection of foods. Plus they take credit cards, unlike Albert Heijn, as was pointed out above. I heard some complaints from locals that they are more expensive, but I did not really see a difference.
Marqt only accepts credit/debit cards, no cash is accepted.
Foodhallen is only about a 15 minute walk or 5 minute tram ride to Vondelpark. Personally, I'd opt for getting something there over going to Albert Heijn or other grocery stores that have pre-made sandwiches. Or, I'd find something to eat at Albert Cuyp Market and picnic in Sarphatipark and then head to Vondelpark later.