-You can buy products and services with your btcs from sites like Overstock, Expedia etc.
-You can exchange your bitcoin for traditional currency
-You can lend your bitcoins
Bitcoin has many online applications. Gambling sites including casinos, trading sites, betting sites etc. are some examples where bitcoin has established a foothold.
Apart from investment, trading is one of bitcoins largest application or any other crypto-currency for that matter. If you already have a secure amount of investment with bitcoins you can always go to the above mentioned sites to earn even more bitcoins and increase your stockpile on a daily basis.