Insertable come in two main flavours in my book, pleasant and painful (or at least uncomfortable), there some cross overs but mostly that it due to the size.
So I'm guessing based on your previous posts you're more into the pleasant ones, so here is a few I like.
Carrots, come in big and small. The smaller ones can be used in multiples to slowly stretch you open. Try using the big end first (works really well with a bunch of small ones) as it helps them stay in place. You can also try cutting notches out of the sides for a cheap, DIY ribbed dildo.
Hard boiled eggs. Obviously eggs come in various sizes so start with you know fits. To start out put them in a condom so you can easily pull them out again. For a fun evening game though insert a couple then get your bf to fish them out. Could take a while.
Gold balls can also be substituted for the above eggs.
The fruit salad game, chop up a variety of fruit or get small things like strawberries, grapes etc. Have your bf fill you up then use a long spoon to fish it all out again, its up you if you or he eats it or you both do?
The stuffed sock. Get a sock and place over a slim dildo, push the sock deep inside then withdraw the dildo, now fill the sock with lots of small things, marbles are good but small stones, nuts or anything similar will do. When full see if you can pull the full sock out again. This is a basic version of a "birthing" game.
That should get you started.
