a small token of one's sentiments; a humble phrase used when giving a gift (often followed by ～ですが).
ほんの気持ちですが、受け取ってください。
It's just a small token, but please accept it.
お世話になったお礼に、ほんの気持ちをお渡しします。
As a thank-you for your help, I'd like to give you a small token.
ほんの気持ちですが、と言って手作りクッキーを差し出した。
She said, 'It's just a small token,' and handed over homemade cookies.
just a little; only slightly (used adverbially to indicate a very small amount or degree).
お礼の気持ちですから、ほんの気持ち程度の金額です。
It's a token of appreciation, so it's only a small amount of money.
手伝いはほんの気持ちですが、役に立てば嬉しいです。
My help is only a little thing, but I'm glad if it's useful.