it's not much, but ...
A humble set phrase used when giving a gift, downplaying its value to show modesty. Often followed by どうぞ or お受け取りください.
It's not much, but please accept it.
This is just a little something, but please help yourselves.
Literally 'it's a boring thing, but...', from つまらない (boring, trivial) + 物 (thing) + ですが (but it is). The phrase uses humble language to modestly downplay the gift.