meal ticket n.
1. [late 19C+] (orig. US) anyone good for the price of a meal.
2. [late 19C+] (orig. US) anyone who provides money or a livelihood for someone else, who thus needs to make less effort; also the object which earns one’s income.
3. [late 19C+] (orig. US) employment, wages, whatever provides the price of a (fig.) meal.
4. [1950s] (US) a personal preference.
5. [1960s+] (US gay) as senses 1–3 above, in homosexual contexts.
6. [1970s] an opportunity.