You can use regular grass seed in trays, mine stay outdoors and use the trays just ahead of them getting back outdoors and belly preparedness for grass.
you can also buy specific grass seeds to plant but can’t recall the same as mine were just normal and the wheekers love them. Worth signing up to the Guinea Pig Magazinr for stuff like that - lots of great ideas.
I just buy the £1 boxes of seed from Poundland. I use seed trays or any pots I have. I discard the first cut of grass from the seeds as the pack tends to contain growth accelerants that may affect the grass. You can buy animal grass seeds on line but it's an expensive way to do it. I found the cat grass to only give a good growth once after it was cut it was very slow growing.
Have a try at growing lettuce in trays or individual pots too, they do very well and you can just pick a couple of leaves when you need them. Pepper seeds can also be planted in pots if you have a sunny sheltered corner outside or window sill. I experimented with a few seeds out of a pepper last year and managed to grow full pepper plants with good size peppers on them