Although Murch has already given an excellent high-level answer, I'll add on some more details as an avid collector.
The first step is identifying the kind of item you have. This is going to fall into, broadly, three categories.
Bitcoin themed-tokens - These are a dime a dozen, and sold on common marketplaces like Amazon, Etsy, etc. They're simply metal coins or bars with Bitcoin stamped on them, typically accompanied by a design of a face or circuit board on the back of the coin. They have no identifying marks (such as a hologram, serial number, QR code, or bitcoin address), and as simply commemorative tokens. They contain no Bitcoin inside them, and are functionally no different from an arcade token.
Commonly, they look something like this
Loaded Bitcoin Token - Loaded tokens have been made by a handful of creators over the years, most famously Casascius. Other makers with sizable quantities produced (and thus more likely to randomly crop up like this) are BTCC, Satori, Lealana, AlpenCoin, and Denrium. Many other smaller series with tens or hundreds of pieces produced exist as well.
Identifying a specific series can be hard without photos, but you can look for indicators that it is a collectible item - it will typically be made of metal (Brass, Silver, Titanium, Copper, and in some cases a mixture of them), Clay or Plastic (usually, these take the form of poker chips from Satori, BTCC, or MoonBits). It will usually also mention the name of the creator (such as "BTCC" or "Casascius"), and come with a holographic sticker on some part of it (for coins, usually at the back - for bars/blocks, usually in one corner of the face). The sticker may or may have a small window in the middle showing the first few characters of a Bitcoin address). The holographic portion itself may contain some or all of the address, and may be marked with a serial number. You may have to try viewing the sticker from multiple angles to reveal text or finer details, as it may not always be visible head on.
In the event that the token has a unbroken holographic sticker, it is possible that it contains a BTC value - the sticker typically contains a private key behind it, which has an associated bitcoin address. In many cases, this address is loaded. However, several series have been made over the years that were sold as "Buyer Funded", where it is up to the eventual owners to decided whether or not to send BTC to that key.
Redeemed Loaded Token - It is also possible that you have an item which has a holographic sticker that has been peeled (look for honeycomb patterns or the term "VOID" appearing in the sticker), or have had the sticker removed entirely (look for a suspiciously blank spot which would be good for pasting a round or square sticker and stands out from the otherwise patterned/design heavy body of the rest of the item). In this case, any BTC it may have contained is likely gone, but the redeemed item itself may be worth a small amount of money as it is still typically collectible.
If you find your item falling into categories 2 or 3, it is best to try to identify exactly what you have - some of them can contain sizable amounts of BTC (0.0001 through 1 BTC are common, with amounts above 1 BTC being fairly rare).
I have built a site at collectible.money that indexes a significant portion of the most common/well known creators and items - if you find any identifying marks such as the name of a creator, series, partial/full BTC address (look for a string of random looking characters starting with 1, 3, or bc1, the search function on the website may help to narrow down which item you have (and potentially report the balance, if any).
It is also advisable to post photos to https://bitcointalk.org/index.php?board=217.0 - the Collectibles forum on Bitcoin Talk is fairly active, with many extremely knowledgeable folks who are aquatinted with nearly the entire spectrum of Bitcoin collectibles. Make sure to avoid responding to any 1:1 messages, and if you are uncertain about the status of your item's funding, cover up any QR codes/paper/stickers - simply posting the face of the item will usually be sufficient for folks to identify it.