I have a Crouse-Hinds main load center. The ground bus is at the top left of panel and the neutral bus is at the bottom right of the panel. I want to add a 15 amp circuit for two outlets in my garage. The ground bus bar terminals are full. My question is can terminate my neutral and ground wire both to the neutral bus bar as long as they each are different terminals on the neutral bus bar. This load center is main panel and not a subpanel.
Mixing Grounded and Grounding
If this panel serves as the main disconnect, and the grounding and neutral bus bars are bonded. Then yes, you can terminate both grounded (neutral) and grounding conductors at the same bus bar.
Notice that the bus bars are bonded using a bonding strap.
Multiple Conductor Terminals
If the bus bar is able to accept multiple conductors under some or all of the terminal screws, it should be labeled as such either on the bar itself or in the panel documentation. Terminating multiple conductors under a screw that is not rated for it, can cause bad connections, excess heating, damage to the conductors, etc.
Additional Bus Bars
Some panels are configured to allow additional bus bars to be installed. If your panel is one of them, you could install an additional bus bar and terminate extra conductors there. Other panels may accommodate extended (longer/larger) bus bars, that can be installed in place of the existing bus bars.
Because it is a non-subpanel, you can put both ground and neutral in either bus bar. However, an inspector could possibly be persnickety and require they be split, especially if it is a small load center which looks ripe to become a subpanel some day.
If required to keep the grounds separate from the neutrals, it is usually okay to place a pair of wires in one terminal as long as both are copper and the same gauge. Inspectors don't like that, but they understand (in my experience) as it is better than the alternatives.