What does 'wick' mean as a suffix in place names, such as Warwick?

Wick derives from Norwegian "vik", meaning "bay".

http://sinclair.quarterman.org/glossary/glossary.html

Warwick itself was named from a feature and means dam farm (Baloo is not swearing):

http://www.behindthename.com/name/warwick

In short, -wick means "a place where goods are traded" or simply "a market"
"Vik" is an old scandinavian word meaning "cove" (or "bay")

https://en.wikipedia.org/wiki/Vik_%28disambiguation%29
https://en.wikipedia.org/wiki/Cove

In Scandinavia, and especially Norway (which is full of coves and fjords), such a cove was the place where farmers would come down to sell the produce of their farms.

https://en.wikipedia.org/wiki/Staple_port
(in this case, the staple was by geographical necessity, not by royal order).

The ships would then ditribute those goods. The people doing this were called "vikings". They built trading settlements near existing cities which were also called "vik". For example, Dorestad was a very wealthy medieval town which was sacked by the vikings several times, but the trading place they built (Vik by Dorestad) is still existing today.

https://en.wikipedia.org/wiki/Dorestad
https://en.wikipedia.org/wiki/Wijk_bij_Duurstede

Since the Angles, Saxons and Vikings all were of germanic/scandinavian origin (northern European coastal areas), they all would have used the word Vik.

"Wick" comes from the Norse "Vik", for "bay", quite common in Norway. In local dialect "Wick" is pronounced "Week" - much closer even to modern Norwegian.
http://sinclair.quarterman.org/glossary/glossary.html