This paper presents simple opportunistic relaying strategies with decode-and-forward (DaF) and amplify-and-forward (AaF) under an aggregate power constraint. The focus is on distributed relay selection using only local channel knowledge. It is shown that opportunistic DaF relaying is outage-optimal, equivalent in outage behavior to the optimal DaF strategy that uses all potential relays. Opportunistic AaF relaying is also outage-optimal among single-relay selection methods and outperforms equal-power multiple-relay AaF strategies with local channel knowledge. These findings demonstrate that cooperation provides diversity benefits even when relays do not transmit but instead act as passive relays, prioritizing the transmission of a single opportunistic relay. Numerical and simulation results validate the analysis. The paper also discusses the benefits of proactive opportunistic relaying, which allows most relays to enter an idle mode during source transmission, reducing reception energy costs. The results show that relays can be useful even when they do not actively transmit, provided they follow the "opportunistic" cooperation rule. The study highlights the importance of cooperative diversity and the effectiveness of opportunistic relaying in improving network performance.This paper presents simple opportunistic relaying strategies with decode-and-forward (DaF) and amplify-and-forward (AaF) under an aggregate power constraint. The focus is on distributed relay selection using only local channel knowledge. It is shown that opportunistic DaF relaying is outage-optimal, equivalent in outage behavior to the optimal DaF strategy that uses all potential relays. Opportunistic AaF relaying is also outage-optimal among single-relay selection methods and outperforms equal-power multiple-relay AaF strategies with local channel knowledge. These findings demonstrate that cooperation provides diversity benefits even when relays do not transmit but instead act as passive relays, prioritizing the transmission of a single opportunistic relay. Numerical and simulation results validate the analysis. The paper also discusses the benefits of proactive opportunistic relaying, which allows most relays to enter an idle mode during source transmission, reducing reception energy costs. The results show that relays can be useful even when they do not actively transmit, provided they follow the "opportunistic" cooperation rule. The study highlights the importance of cooperative diversity and the effectiveness of opportunistic relaying in improving network performance.