Most US states, including Florida and Texas, now have kiosks (usually at locations like grocery stores) where you can register your vehicle. If you are unable to renew online, anyone you trust within your domicile state would be capable of renewing the registration for you and collecting the sticker from a kiosk.
Florida: Renew online or use a self-service kiosk located within the state, or have someone you trust in Florida renew on your behalf.
Texas: Renew online or use a self-service kiosk located within the state, or have someone you trust in Texas renew on your behalf.