Which is lightest on resources, free and portable MP3 player for Windows with playlist support? [closed]

Use an older version of Winamp from the 90's ;)

I think foobar2000 suits your needs

Wikipedia on foobar2000:

foobar2000 is a freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. It is known for its highly modular design and extensive SDK which allows third-party developers to do such things as completely replace the interface. While supporting a large number of audio file formats, it has many features for metadata support and file organization, and it has a converter interface for use with command line encoders. To maximize the audio fidelity of consumer-grade equipment, it provides noise shaping and dithering. It features a number of official and third-party components which add many additional features. While the core is closed source, the SDK is licensed under the BSD license.

XMPlay is pretty good. Very lightweight, skinnable, no install needed.

XMPlay is an audio player, supporting the OGG / MP3 / MP2 / MP1 / WMA / WAV / AIFF / CDA / MO3 / IT / XM / S3M / MTM / MOD / UMX audio formats, and PLS / M3U / ASX / WAX playlists. A load more formats are also supported via plugins. When XMPlay was first released in 1998, only the XM format was supported, hence the name "XMPlay".

XMPlay is freeware.

Another small and lightweight player is musikCube, which supports playlists as well as dynamic playlists:

musikCube is freeware.