Take yourself into the city for a Koffee at one of the many shops.

Seriously though 7 hrs is plenty of time. There is a station located under the arrivals hall where you can catch a train direct to Centraal Station in Amsterdam takes approx 15/20 mins. Here you will arrive right in the middle of the city.

There are lockers in the arrivals hall where you can store luggage/carry on untill your return later in the afternoon/evening.

There is plenty to do depending on what floats your boat.

IIRC this topic has been discussed in detail before many times on the KLM and NWA boards try doing on search on them for further tips etc.

Cheers