yes there is; investments like buying guns to arm your antifascist and red guard friends; putting money in strike funds and bail funds; buying books (or printer paper and ink) to help comrades engage in theory and host study groups or print agitprop material to distribute and poster...

but yeah "marxist stock-trading" is an oxymoron. You are being the opposite of a communist; you are becoming a petty capitalist contributing to subsidizing the big capitalist's exploitation of labor, in exchange for dividends off of generated profits ie exploited surplus value created by labor; and trying to leverage other petty and big capitalists' confidence in the stability and growth of profits to sell for higher than you bought.

Aside from it being contradictory on its face to "stock-trade like a communist", I'd feel dirty as hell if I spent time and effort using the tools of liberation that are dialectical and historical materialism to analyze the confidence-game ponzi-scheme that is capitalist stock market and gamble on stocks(which again, the value and its fluctuation comes from real and expected profitability; that is, the surpluses and stability of growth of these surpluses that can be expected to be vampirized from exploited labor) rather than on exposing the most critical points of contradiction and agitating and organizing their rupture to the benefit of the communist movement.